My price was lower at MAG as well. When I had the problem with Kelly I went to MAG and they matched the deal -and even went less by $500!
Since I still have a 2001 X5, I have been to both service departments a bit more than I would have liked, but also both about an equal number of times. I must say that they both are good but expensive. No complaints really with either dealership from a service perspective.
BTW.... Eric (sales manager for Kelly) was also very professional with me, right up until I informed him that I bought a 2006 325i from MAG. Hey, he has a job to do so I hold nothing personal but just know that those puppy dog eyes are part wolf.
I suggest going with MAG but hey, that's just me...