MVC 2
Regarding microsoft products (imho):
Version 1 is a beta - buggy and incomplete. Version 2 is what vesion 1 should be.
I am using MVC 2 RC for a very big CMS project and haven't had any issues. If you don't know MVC version 1 very well, I would go MVC 2, so you don't end up having to learn the old stuff and the new and get all confused.
I can attest that 2 is stable in my experience and I think the new features make it worth the risk. (Ask me again in a month after my project is LIVE :P )
UPDATE: Project is now live and running great on MVC 2. A full featured running on MVC 2 handling tens of thousands of users per day. NOW is the time to jump into MVC 2, it is awesome!!!