Huge fan of both 2nd and 3rd/DC editions - 3rd/DC edition being my favorite gaming system at the moment. Haven't had any problems using it for a variety of games of a variety of power levels, though I admit 2nd had some power creep and imbalance issues. The changes for 3rd helped smooth things out a bit. For me, it has the right degree of balance and granularity, which is rare in any system. Never played the 1st edition, so I can't say whether it was good or not.
M&M is very easy to play and run, especially in comparison to the Hero System. I've been a Hero fan since the early-mid 80s, but admit that the game has gotten out of hand. If you didn't follow Champions/Hero through its evolution, it'd be incredibly difficult to learn and play now. Plus, there's a huge grumpy old gamer schism between 5th and 6th editions (and a smaller one that still won't let go of 4th). I like the changes in 6th edition, but there's just too much granularity in the system at the moment. M&M is the way to go.