I like both apps for different reasons, as both have minuses and pluses.
Vegas:
The ability to work on simple composites inside Vegas is a plus, but its unique interface kills me. Even with the so-called updates in Vegas 6, it still lacks the ability to nest sequences. I know you can import Vegas projects, but that’s not enough these days.
I also like the responsiveness of previews in Vegas.
Premiere:
Since its UI is more standard, I work faster in Premiere. The integration with other Adobe products is something Sony should try to improve with Vegas, Acid, Sound Forge.
Also when choosing a system, you should also consider 3rd party support – Premiere scores another point here.