check out the uspsa equipment survey that spells out what guns everyone is using in the various divisions, might give you some ideas.
i guess first thing is what division do you want to play in. 9mm is the logical/majority choice in production, with .40 being the logical/majority choice in limited.
9 also is a great choice for 3 gun, steel matches, idpa and the like. .40 works in these games (and uspsa production) but you're at a recoil disadvantage unless you reload or buy minor power factor ammo.
as far as 17/22 vs longer 34/35, i think the surveys show the longer versions being more popular, but it is certainly a personal choice. shorter seems to point better but longer has longer sight radius. both have tons of aftermarket parts and accessories. i changed all my glock sights out to warren sevigny competition fiber front and wide rear notch.
i'd say find a range that has all four glocks and give them all a shot or 50 and see what you like best. frankly if you like your current 9mm that may be the best and easiest choice. using one gun for everything will give you consistency which is a good thing, but we all like having a few toys to use for various applications.