This is always a tough decision and depends on your needs.
Revo is definitely the future (although Evo will be around for a long time) and the latest Revo builds are relatively stable. Not all the add-ons are translated, however, (e.g. no MaxiGallery) so something you need might be missing. If you go with Revo, you might want to wait for Beta-4 which should be out in a week or two.
In addition, the permissions system is quite different in Revo and the documentation on it is still fairly sparse. I’ve tried a couple of times and I still don’t understand it. That goes both ways, though. If you have complex permission needs and multiple users, it may be harder to convert the site to Revo than to start in Revo.
If your site is relatively simple and you won’t be making major changes to it, you could just stay with Evo. If you have complex snippets and/or plugins in mind, Revo might be a better choice as long as the add-ons meet your needs.
I hope this has done you more good than harm.

It’s tough to calibrate answers to the Evo/Revo question.