Jacket And Pants

1. Materials and structure

An extensive discussion about outer layer construction materials can be found there. The only thing to add here is that, according to my opinion, synthetic jackets are more flexible in use since they' re not so tight, they' re lighter and they cover a larger portion of the body. As for the pants, a leather one may a safer choice since skin is completely naked under it and abrasion is more cruel when sliding on the ground.
Structure is always the same. The outer layer is a semi- or full waterproof abrasion resistant material. When there is an intermediate breathable membrane (Gore-Tex), the product is 100% waterproof. The inner layer consists of a thin (usually perforated) lining and a removable thermal insulation.

2. Protection

An extensive discussion about crash protectors can be found there. The most sensitive parts of the body that must be protected are the following:
Back, elbows, shoulders, for the jacket. Look for hard pads like the CE approved ones. Be sure not to wear a loose fitted jacked, otherwise pads will be displaced in case of an accident. If the jacket you want to buy is not equipped with a back protector, you can have a kidney belt with back protector, a very good alternative.
As for the pants, it must have hard CE approved pads on the knees and legs (additionally, they help against cold). However, be sure these protectors don't make you feel uncomfortable when sitting on the seat.
CLOVER and BMW produce pants with hips/thighs protectors.

3. Rain - cold.

There will never be an all-season cloth. Thus, your number of choices is just a matter of money. If talking about waterproof clothes, see the page about water-tightness. Cordura can be semi-waterproof if it is Teflon or polyurethane coated. Pay attention to sleeves and trouser legs: top of the gloves must be worn inside the sleeves and top of the boots must be inside the trouser legs. In the opposite case, water will flow from sleeves into the gloves and from trouser-legs into the boots (what a waste of money for the waterproof membrane!). However, it's difficult for leather pants to satisfy the above requirement.
Any serious cold-defeating cloth must include special thermal insulation (thinsulate, aluminium foil etc). It's light-weight, removable and it removes the need for many layers of internal clothes (at least for ambient temperatures over 0^oC). This insulation is very effective when fitted inside the pants (jeans are completely intolerable when chill factor starts to be considerable. Waterproof membrane gives an additional help here (and it would be nice if it's removable). A removable insulation is a "must" for the summer.
Check on the jacket a) if the collar protects neck from the cold sufficiently, b) if main zip is not directly exposed to water. As for the collar, it's again difficult to find such a leather jacket.

4. Heat

Things are going tough in that case. Full waterproof, full protected clothes are not the best means against the summer heat in Greece. My black coloured jacket (a CLOVER Hydro) has removable waterproof membrane (BMW also makes a similar product). Even so, I can't stand it when temperature exceeds 25^oC (77^oF). I never found trousers with a removable membrane.
It would be better if the jacket is light-coloured and ventilated. You could easily find such enduro type with many ventilating zips on sleeves, chest, back and armholes.
May be leather it's better due to it's insulating - perspiring features, if someone could find a "ventilated" model. Anyway, whatever clothe you use, it's better from the bare skin.

5. Convenience

Synthetic jackets usually have many zips, belts, Velcro straps to adapt them to our body shape and many useful pockets. Protector pads are usually removable, this way you can easily inspect or replace them with  hard ones (if they 're not already of this type), Washing is also easier when pads are removable.
Be careful: if your jacket or pants include a waterproof foil, you usually cannot machine wash them ("Miporex" membrane is a known exception to that rule). After washing, dry out very carefully and never fold them aggressively (you better avoid folding at all).
Every synthetic material jacket must have a belt to tighten the cloth around the waist area. Lower and hand buttons must be preferably covered with elastic material to avoid scratching gas tank.
Knee protectors must not obstruct leg motion neither squeeze knees when you are on the seat. E.g. synthetic pants model WP from CLOVER has neoprene knee protectors: a hardly flexible and excessively tough material for that kind of use.

6. Reflectors

Indispensable at night, they help us being visible by the other drivers, when ambient light is not adequate. Some reflectors are ugly enough to make us not buy that cloth. Other ones are visible only when artificial light hits them (e.g. CLOVER Hydro).
Passenger must wear the same very reflective clothes, for obvious reasons. In case these reflectors seem inadequate, you can use extra reflecting tape (like Scotch-Lite).

Jacket And Pants

1. Materials and structure

An extensive discussion about outer layer construction materials can be found there. The only thing to add here is that, according to my opinion, synthetic jackets are more flexible in use since they' re not so tight, they' re lighter and they cover a larger portion of the body. As for the pants, a leather one may a safer choice since skin is completely naked under it and abrasion is more cruel when sliding on the ground.
Structure is always the same. The outer layer is a semi- or full waterproof abrasion resistant material. When there is an intermediate breathable membrane (Gore-Tex), the product is 100% waterproof. The inner layer consists of a thin (usually perforated) lining and a removable thermal insulation.

2. Protection

An extensive discussion about crash protectors can be found there. The most sensitive parts of the body that must be protected are the following:
Back, elbows, shoulders, for the jacket. Look for hard pads like the CE approved ones. Be sure not to wear a loose fitted jacked, otherwise pads will be displaced in case of an accident. If the jacket you want to buy is not equipped with a back protector, you can have a kidney belt with back protector, a very good alternative.
As for the pants, it must have hard CE approved pads on the knees and legs (additionally, they help against cold). However, be sure these protectors don't make you feel uncomfortable when sitting on the seat.
CLOVER and BMW produce pants with hips/thighs protectors.

3. Rain - cold.

There will never be an all-season cloth. Thus, your number of choices is just a matter of money. If talking about waterproof clothes, see the page about water-tightness. Cordura can be semi-waterproof if it is Teflon or polyurethane coated. Pay attention to sleeves and trouser legs: top of the gloves must be worn inside the sleeves and top of the boots must be inside the trouser legs. In the opposite case, water will flow from sleeves into the gloves and from trouser-legs into the boots (what a waste of money for the waterproof membrane!). However, it's difficult for leather pants to satisfy the above requirement.
Any serious cold-defeating cloth must include special thermal insulation (thinsulate, aluminium foil etc). It's light-weight, removable and it removes the need for many layers of internal clothes (at least for ambient temperatures over 0^oC). This insulation is very effective when fitted inside the pants (jeans are completely intolerable when chill factor starts to be considerable. Waterproof membrane gives an additional help here (and it would be nice if it's removable). A removable insulation is a "must" for the summer.
Check on the jacket a) if the collar protects neck from the cold sufficiently, b) if main zip is not directly exposed to water. As for the collar, it's again difficult to find such a leather jacket.

4. Heat

Things are going tough in that case. Full waterproof, full protected clothes are not the best means against the summer heat in Greece. My black coloured jacket (a CLOVER Hydro) has removable waterproof membrane (BMW also makes a similar product). Even so, I can't stand it when temperature exceeds 25^oC (77^oF). I never found trousers with a removable membrane.
It would be better if the jacket is light-coloured and ventilated. You could easily find such enduro type with many ventilating zips on sleeves, chest, back and armholes.
May be leather it's better due to it's insulating - perspiring features, if someone could find a "ventilated" model. Anyway, whatever clothe you use, it's better from the bare skin.

5. Convenience

Synthetic jackets usually have many zips, belts, Velcro straps to adapt them to our body shape and many useful pockets. Protector pads are usually removable, this way you can easily inspect or replace them with  hard ones (if they 're not already of this type), Washing is also easier when pads are removable.
Be careful: if your jacket or pants include a waterproof foil, you usually cannot machine wash them ("Miporex" membrane is a known exception to that rule). After washing, dry out very carefully and never fold them aggressively (you better avoid folding at all).
Every synthetic material jacket must have a belt to tighten the cloth around the waist area. Lower and hand buttons must be preferably covered with elastic material to avoid scratching gas tank.
Knee protectors must not obstruct leg motion neither squeeze knees when you are on the seat. E.g. synthetic pants model WP from CLOVER has neoprene knee protectors: a hardly flexible and excessively tough material for that kind of use.

6. Reflectors

Indispensable at night, they help us being visible by the other drivers, when ambient light is not adequate. Some reflectors are ugly enough to make us not buy that cloth. Other ones are visible only when artificial light hits them (e.g. CLOVER Hydro).
Passenger must wear the same very reflective clothes, for obvious reasons. In case these reflectors seem inadequate, you can use extra reflecting tape (like Scotch-Lite).