I would recomend use the engine that it's more familiar to you ..
You will found yourself stuck in the middle of nowhere with a engine ( or Cruiser ) failure and folks around you, few trying help with no idea what to do .. and others trying get your buck easy .. with the same absolutely no idea what to do to solve your problem ..
So know first now the plataform that you wanna use and then you can start a trip ..
One more thing . .. X3 ( or was 4
) ini the 1HZ and H55F .. the best milleage in the most popular engine around the world ..