Unless you are racing just get the newest ones you can get on e bay.

A new set of wets is about 250 quid. Used 120 / 180's on e bay generally go for about 50 quid. For trackdays used one will still be much more capable than you will be willing to push them.

Make sure the tread edges are still sharp, anything with visible wear has been used on a drying track.

Doesnt really matter about which make unless you are buying new. I have had Pirelli and Bridgestone both are good. For a few wet track sessions a year you wont use them enough to develop a preference.

That is the other thing unless they are already well shagged only use them when there is standing water . torrential rain type conditions a few laps of a damp / drying track eats them.