Depends. Rumor is that the new Xbox won't have a disc drive and will be strictly digital. This would be in an effort to curb selling used games and confining DLC, and would also allow zero backwards compatibilty It's complete speculation at this point, and the further along the system is in the design process, I imagine there will be significant backlash, because it's not a great design choice.
If its true, it might be worth it, as there are some games you just won't be able to play on the new system, although I imagine the big 360 titles will be available for download.
If you're gonna get one, 360 would be a good choice. There's a solid library, a good online community (if you can get past all the 13 year olds yelling "faggot" constantly), and the kinect is actually a good time, if you care to spend the extra money. If you're into multiplayer, the community is large enough where I see it sticking around well into the next system's generation. And if you're more into single player, there are a lot of awesome games you have to catch up on.