Last night I held a Glock 21 & 21 SF. Up till this point in my life I've only held the regular models, but last night after holding the "small frame" model I was really taken back. The sights on the regular model didn't line up at all when I pulled the gun up, but when I did the same thing with the SF model it wasn't nearly as bad at all, and the grip felt better overall. The SF model also had the ambi mag release on it which is nice to have. Now that there's a glock out there that seems to fit me better I may have to get back on the wagon.
Now the only debate is 21SF in 45acp, or 20SF in 10mm.