UM because I'm not a "fanboi." I really trust Jeff's work. More power with less boost and more linear/smoother delivery than APR? Yea that's there.
Other than that? I've lost respect for APR with their price gouging, ridiculous markups, and their representative on this forum trying to bash other tuners in their own threads. That's why I'm at Forge Twintake over VWR intake, Autotech hpfp over APR's ridiculous price for one, and UM tune.
Other than what's stated in my first "paragraph," I guess everything else is subjective/perspective.