Seam 2 is the current production ready release of Seam. If I were you I would start with Seam 2. Its stable and there is quite a bit of material round to learn it. Seam 3 is still under active development and based on the release schedules I wouldn't want to start using it for about another 12mnths (but thats just my opinion)
Thank you very much for your advice. I really appreciate it.