If you're looking for new, there are 4 engine options in the U.S.
1. 35i (I6 Single Turbo)
2. 35d (I6 Turbo Diesel)
3. 50i (V8 Twin Turbos)
4. M (V8 Reversed Mounted Twin Turbos)
I have the 35i (aka N55 engine or I6 Single Turbo). It's a good balance of performance and fuel economy. You'll have to specify what you're looking for, the the forum members can help.
The engine comparison can be found on
www.bmwusa.com and many automotive websites
