Sorry, but very few AE users around here have used both the NLE's you're asking about.
In AE-Land, Vegas has the reputation -- whether it's warranted or not -- of being a hobbyist application, so AE users shy away from it.
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA
I've used a lot of Vegas, Premiere and AE. Vegas is pretty good. Premiere CS4 sucks hard due to instability and clunky interface. CS5 is a little more stable, but still the interface is clunky. AE is great and stable. I have not used FCP, but have heard from dual FCP/vegas users that they like vegas better.
My workflow is now:
Vegas, export cut to AAF, Convert AAF in premiere, Import in AE, Render with x264 (h264) or hcencoder (mpeg2).