Burris Fullfield II is my favorite scope I've used. I have, however, read a lot of great things about the Vortex scopes. I wouldn't hesitate to go for a Vortex Diamond back or even the higher end one. I can't think of the name for it right now though. I'm not sure if my next scope will be a Vortex or another Burris. I love the Burris and know I love it and it has the reputation to back it up. However, the reviews of the Vortex are just amazing. I would also check out the Bushnell Elite 4200 however, I'm not sure if it's what I'd end up with or not. I think Amazon did have a really good deal on them for like $250 but I think it was a 3x9 one. I'm not sure if they still have that deal going on or not.
These scopes are all cheaper than what you plan to spend but it's a great write up about them. Worth checking out.
http://www.opticstalk.com/forum_posts.asp?TID=21176