New Rails project, which version?

I’m planning on starting a new rails project, should I go with 3.1 or
the current stable release?

FYI, the project is just in the design phase right.

There are some big differences between the stable release and 3.1. You
should research both before deciding. Personally, I am staying well
away from 3.1 until it becomes a stable release. 3.1 incorporates a
different way of working with MVC in terms of placement and templating,
and also uses SASS and coffeescript. There are some great benefits, but
also some considerable changes.

I just had the same question and have opted for 3.1rc4