Why it's better UT than Unreal?

UT is essentially the same engine, yes. But it does feel a lot different. It's more of an action oriented game. Unreal was more of a thinking persons game. You really had to think about where you were gonna shoot if you expected to hit anything.

There are some differences in the editor though. Mostly fixes like Permantly Transform works. Sheering works to a minor extent. Plus you get a few more textures to work with, albeit it's not nearly as organized as the Unreal set. Sometimes it's tough to find what you want (this is where I take the time to load all of them up).

And even if you don't like UT you can still use it to make Unreal SP maps and distribute it throughout the UT community. This can be done by using one of the Unreal GameInfo's in the DefaultGameInfo setting.