Good gameplay and variety.
I was never able to play it online with a 56k modem.
The Bottom Line
UT, if you think about Q3 comparing is graphically inferior. It do has awesome graphics, but can't compete with Q3. It's slower, like many Q3 lovers complain, exclusively because Q3 runs on Open GL. UT in Direct 3d. If you look around the web, you'll find good Open GL drivers for UT and it'll be as fast as Q3.
The stages are way better designed and varied. Q3's are good, but lack theme variety. UT also has a lot more of game types and if you say: What about mods? Comm'on! We're reviewing a game, not it's community!
Weapons? UT's got a lot more, and even if you say only a few are useful, Q3 runs around only 3! Rocket launcher, Railgun, BFG! Sometimes the Shotgun. And UT's are, at least, more creative...
So... you'll probably have lot's of fun with both games, but with UT It'll probably last longer.