I haven't driven the 4.4i, but that's the one I'd get. The 3.0i is good enough for city driving, but it lacks the real guts when you have to make a quick turn at an intersection or when you need to merge right NOW in front of an 18-wheeler on the freeway.

Gas mileage may vary, but in most circumstances the 3.0i will get better mileage. On highway stints, the V8 may be slightly better since it doesn't need to work as hard and is geared taller.

Both handle pretty good for SUVs, and both have relatively close 50/50 weight distribution (an attribute of all BMWs). I'd say go for the V8 if you can.