I have both a Tactical and Compact, and I like them both, although admittedly the Compact is unnecessarily large for CCW, which seems to be its main purpose in life. Fortunately, I'm a big guy, and with a decent belt slide, I can carry the Compact acceptably well. It's been my CC gun of choice for a while now.
The Tactical has the same match trigger and adjustable sights at the Expert, and also has an O-ring barrel (although it's not the same as the Expert's barrel, which has the O-ring in a different place). It shoots great, but I haven't fired an Expert and so can't comment on it. I'm not convinced that it's worth paying the extra money for the longer slide and ambi safety you get with the Expert (in fact, since I don't like ambi safeties, I regard that as a drawback for the Expert when compared to the Tactical). If you get the Tactical, check with Capital City Firearms in Richmond, Va., for some neat accessories for it (thread protector, flash suppressor).
Also, if you want a Tactical, move fast -- Tacticals aren't being imported into the US any more (and may in fact be discontinued, although it's tough to tell -- HK makes lots of stuff that they don't sell in all countries). The Compacts are plentiful, at least here in NC.
Final tip: You'll find a reasonable selection of holsters marked for the USP .40, but they'll also fit the .45.
[This message has been edited by David Roberson (edited February 25, 2000).]