Vraciu, the AH1 skins still in the game are the Ar 234, Me 163, Val, Kate, A-20G and Boston, F4F-4 and FM-2, Ki-67, Ju-88 and Tempest. These will likely be updated in the near future and are pretty dreadful shapes to skin anyway, lots of stretching, mirroring and distortion. So basically avoid these.
The AH3 shapes are the 110C and G, TBM, SBD-5 and Ki-61. These are all 2048 res and have the full set of effects files.
The rest are AH2 skins. These are 1024 res or 2048 for the big bombers. They don't have the issues of the AH1 stuff, little or no mirroring and stretching etc. The earliest AH2 shapes tend to be the most popular rides in the arena, the US and German fighters, the Spit series, the Ki-84 and the big US bombers. I expect these may well get updated next once all the AH1 shapes are all done.
Looking through the skins page there aren't many rides that are approaching full, most of the 109s, the 190A-5, the Ki-84, the Spit V and IX, the B-17, 24 and 29. Most of these still have 6-12 slots. The P-47D-11 is the only one full apart from P-51s.
Some rides are kind of boring colour scheme-wise. For instance the Lancaster has essentially one colour scheme with the only variation in skins being nose art and squadron codes. I've found that apart from the USAAF early war aircraft tend to have more interesting and varied schemes than late war ones.
Some rides give you two or more shapes for one template. The P-47 shapes have a lot of similarities as do the Spits etc.
To a large extent its going to be a question of what floats you boat though. Post a few subjects you are interested in and I can tell you the pros and cons of them.
