I was in Phoenix on business a few weeks ago. I stayed at the Westin and absolutely loved it.
http://www.westinphoenixdowntown.com
Depends on how much you're looking to spend, of course. The hotel isn't cheap. I think my company paid $400+ per night or so.
I've stayed at the Hyatt on business before, as well, and it was great.
http://phoenix.hyatt.com/hyatt/hotel...index.jsp?null
It was a bit cheaper, from what I remember. Like $250ish per night vs. $400.