With the exception of Bryce, I've been happy spending weeks in Zion and the Canyon
Bryce is good for a few days. Bryce is best at sunrise - it faces east and you get the best colors and shadows for photograpy at sunrise.
You might also consider Red Canyon which is on the other side of the plateau - 80% of the scenery at 10% of the visitation.
This site:
http://www.zionnational-park.com/ has tons and tons of info for the whole area, and for Zion in particular check out Joe Braun's site.
I often stay in Mt. Carmel Junction when I'm there but Kanab is also centrally located and has more dining options.