If you plan to do any 3D stuff then go with the OS (better throttle response, more power) but you might also want to check out the Thunder Tigre 46Pro. It's cheaper than the OS and better value for money, in my (and many other folks) opinion anyway.

I just put new bearings in one that has already done over 200 hours and when I tached it today, it was just as strong as the one I bought at Christmas (which has about 5 hours on it now).

The TT46Pro can be had for as little as $74 -- at that price it's a real bargain and lots of profile 3D fliers love them.