I can tell you that Remoting 2 is entering the twilight of its lifetime, though I expect it to be in active maintenance mode for a few years. That is, there won't be much new development, but I'll continue to fix bugs. It's in some of our products supported by contacts, so we're obligated to keep it working. So I think it's safe to start using Remoting 2.
Remoting 3 will be the Remoting of the future. David Lloyd could tell you more about the status of Remoting 3, but I believe 3.0.0.GA is missing some functionality. I believe 3.1.0 will be more "featureful", and the next release will be 3.1.0.CR1. I can't tell you when it will appear. Remoting 3 will have the advantage of being in active development, so, if there's a feature you want, you're more likely to get it Remoting 3 than in Remoting 2.