I'm a meat freak. I'd be a butcher if I could afford the school :) Filet mignon is the leanest of all! It's pricey but if it's just a once in awhile thing it's not a big deal. I eat sirloins most often, I buy them at Costco since they're higher quality. A lot of grocery store beef is kind of not great, but if you stick w/ filets at the store you should be OK. I've found that the cheaper cuts, like sirloins, are not that great at my grocery store. I also love a big fat ribeye but it's so good because of the fat content... probably not what you want :)
I also really like flank and skirt steak and tri-tip for grilling. Just cut against the grain, instead of with it, otherwise you will end up with very chewy pieces. Hanger and flat iron steaks are good too, they're just harder to find.
This page might help you: www.clovegarden.com/ingred/ab_cowc.html
Basically, the cuts you see at the front and the back of the cow are generally more tough. Meat is muscle, and the muscles at the front and the back get more use, so they are tougher, and are better for slow cooking and braising, or to grind up to use for burgers. They also are good for marinating. The muscles more in the middle of the cow are used less, so they are more tender. As you can see, the tenderloin is wedged between other ones, so that's why it's so tender. Filet mignons are just steaks cut from the long tenderloin.
Edited by: YOJULEZ at: 4/25/2013 (11:37)