I've tried Cubase, Logic, and Sonar and found their interfaces to be somewhat cumbersome - especially Logic. I think the issue is the apps are too caught up in trying to look like a console instead of looking like a computer application. Vegas looks like a computer app through and through, and I love it.
Anyway, I don't believe it has ASIO, and I know it doesn't have VST support, though I believe both of these are on their way to Vegas as they've been recently added to Acid.
Vegas Video's core is Vegas, when it was just an audio app. Sonic Foundry just added video functionality on top of it, so it functions quite well as an audio app. I did some video work with it for the first time last week and found it was incredibly easy to use - same as working with audio. I heartily recommend Vegas.