If you've got the time, look at the Sony Ericsson Xperia that is coming out.

http://www.networkworld.com/community/node/24935
http://www.expansys-usa.com/p.aspx?i=163460Stu

Between the Tilt and HTC TyTN II, I vote for the TyTN II. It is far more modifiable. The hacker community supporting the phone is incredible. I have an HTC TyTN I (Cingular 8525). I reflashed the phone with the Shap's ROM from XDA and I have Touch Flo, and a number of other features.

Yes, the TyTN series is a little larger, but you can do anything with them. I'm not sure whether the TyTN II or the Blackjack II is faster. Comparing megahertz doesn't really work when different processors are in play.