I think the MI is the best value for the budget minded consumer. It has the high quality machining of KAC (almost), but closer to the price of YHM. I have a KAC RAS, a roommate of mine has the YHM equivilent, and the guy who's place I took in the apt has the MI. The MI is great IMHO. It uses a similar (if not identical) method of attachment as the YHM...the plastic (???) extensions that are insterted into the Delta ring and the end cap, rather than the extensions being an integral part of the rail system.
I still think the KAC is nicer, but I'm not sure if it's as nice as the price difference would suggest...though I'd hesitantly mount optics on the KAC, but not the MI or YHM. My roommate describes the YHM when he puts rail covers on it as "holding an elephant dick", not the case w/ the MI.
As I said earlier, I think the MI is the best value on the market for people on a budget.