In my experience simple parries work best for defending against punches. I prefer to just deflect the punches with open palms instead of covering up. (This is easy with MMA gloves, not so much with boxing gloves.)
As to actual "hard" blocking, a block is a strike, a strike is a block. Knee checks for low kicks and elbows to block higher...may as well bust that hand or foot up and make them pay for throwing it.