That is probably your best best. Try them both and get a feel for both and then make the decision. I have my Xbox still, but after playing the 360 version I don't even have any desire to go back and play the Xbox version. I still have my 06 game as well. It sounds like 07 is very much like 06 as you would expect. To me the gameplay is far and away a huge improvement over what 06 had to offer. I am primarily a dynasty player that usually ends up simming a lot of my games because I like the dynassty aspect of building a small school or working on making the Bruins a dominate program. Usually that means I get a bit bored with the gameplay after awhile and end up simming a lot then playing games here and there, especially the big games. Usually once in my dynasty I don't ever play exhibition games as I just want to spend time with the dynasty. The gameplay for the 360 is so fun I have yet to sim a game and often just pick up and play a quick game out of the dynasty because the games are so fun to play.
The animations, running game, overall feel of the game on the 360 really is new and amazingly fun to me. I see others feel the same way, but you really may not be happy unless you try both. I can't get enough of the gameplay to even want to try it on the Xbox. This game is so good now it really should be something else next year when they add more features to the game. This may be the first time I really am playing the game (not just simming dynasties) right up until the next version comes out.
I also can't believe you have had this much restraint not to buy one of them yet or rent one of them. I had to have it the day it came out, lol.