i currently have a gen 3 17 with a gen 3 22 in route. a gunsmith buddy of mine stippled my 17 and added some sights, did a trigger job and such and its been amazing. i recently added a threaded barrel for it. we got to talking about changes again and i said i had thought about starting with a 22 so i could get the multiple caliber use even though i don't really care for 40 too much. so he took our conversation and built himself a clone of my 17 in a 22 and then got a threaded 9mm conversion barrel for it. after all the fuss, turns out he wants to go 1911 again so im getting his 22 at a steal...
that said, if i get a glock in the future, it will probably be a 40 frame to get the multiple caliber use if only just because.
ive had multiple 34s, 35s, 19s, a 21sf, and a 26 in the past. the 17 with a threaded barrel is by far my favorite setup. my next will likely be a very similar build in a gen 3 21, non-SF.