I use ZF the most.
Though I just started using Symfony2 (still in early development) for a new project. Watch the talk by Fabien for a good overview. It's nothing like symfony1 (which is A Good Thing imo). It's a bit difficult using a framework with hardly no documentation and that changes all...
There are a few valid reasons for keeping www above and beyond that of pure preference. Two that spring to mind:
Cookie control. Cookies set on non-www are accessible on every sub-domain you might have later.
Ability to CNAME www (for example to a CDN). This way you can still keep other...