Hmmm...while I really enjoyed the BMWs I owned, they were a maintenance hassle even within the warranty period. I'm on my second WK2 (2013) Hemi and am closing in on 90,000 miles with no problems and looking to pass this on to charity and get another at the end of the year. So, you guessed it, I'd say do a new Grand Cherokee over a used X5, absolutely.
As a side note, I see many BMWs driving around on seriously hot days with their windows down and owners drenching in the humidity. When opportunity & curiosity got the best of me at gas stations I asked the owners "Why roll with the windows down in brutal heat and humidity?" Every response was that the AC was broken, it was out of warranty and they didn't have a spare $2000 laying around. Yes, avoid the used X5.