I agree with Big Mick about getting a start in standard tuning. For one thing you can recognize chord shapes from other guitarists at jam sessions. But I also agree with Brian, that DADGAD offers good possibilities. I used to switch back and forth at a local song circle, than I got too damn lazy to do that and just kept my guitar in DADGAD. I started playing accompaniments to other people's songs, regardless of the key and that's worked out pretty well. It does prevent the samey issue Brian mentioned. Parenthetically, I heard a couple songwriters who do everything out of G and capo up and down and that sounds pretty samey after awhile, too.