You cannot ask that question. Forced to choose ,my brain would implode.
As far as the most collectible ,that would be the scarcest. Like the 4" 629 no dash. or the 627-0 as you mentioned. Any first run ,624 ,610 ,627, these will only increase in value and collectibility.
Any 625 would be a favorite G frame.(pg. 170 S.c.S.W.3) Be it 45 Colt ,or 45 A.C.P.
But I have become nuts for almost any F 357 these days ,particularly the 3" model 66 and 65.
The X frame has only been produced in stainless, ANY 460, is a out and out winner in my book.
I have to rest now, my head hurts , Regards AlleN-Frame