Corn fed beef tastes better. Not healthy for the cows though. The best is grass fed beef until they're about to be slaughtered, then feed them corn then kill em.
Having eaten both, back to back at a fancy steakhouse, I can say that that's a very subjective taste. Alberta (grass or grain fed) has a stronger flavour, vs. the USDA more delicate flavour. I'm not a steak connoisseur but I prefer Alberta beef.