When I started playing superhero games, the two main contenders for my interest were Champions and Villains and Vigilantes.
Champions had a system for building characters that could incorporate a lot of subtlety, could model a lot of peculiar and highly specific constructions of powers. I don't think any superhero game has come close to its ability in that regard. I remember seeing a version of Cyclops that put his high-powered energy blast on an endurance battery - producing a very good model for the endurance of Cycops' powers as we learned when the X-Men first encountered Arkon and his solar-energy starved work of Polemachus. Not even the Marvel Super Heroes game simulated that level of Cyclops' power.
Champions was, however, sometimes a bear to work with. Characters with broad powers, like weather controllers, were extremely expensive to try to build. The power of its ability to specify very particular powers could also get in the way.
Villains and Vigilantes, on the other hand, was much simpler. By comparison, it was a rules lite superhero game. Powers had a description, did a set range of damage, and you built based on that. Very fast to learn and generate characters by comparison to Champions.
But you could get some significant disparities in abilities, which could make things tough on a GM. You had to be a bit more careful balancing fights when one character had Thor-like powers and another was Hawkeye. That said, it was one game that really did throw together groups of disparate power levels - a convention in comics if you read enough of the Avengers.
In the end, we played way more Villains and Vigilantes than Champions. It was way easier to deal with and faster to get going. It was easier to build the types of characters we wanted to play.
Then along came Mutants and Masterminds. It has a point-construction toolkit of powers like Champions (moreso in 3rd edition than 1st), but I find it a lot easier to buy up a character with broad abilities (like those weather controllers) in M&M than in Champions. When it first debuted, it really felt to me like it split the difference between V&V and Champions quite well - offering a lot of customizability without being quite so Champions-insane about it.
Mutants and Masterminds also incorporates a non-ablative combat resolution that's kind of cool. In Champions, you whittle away a target's Stun and/or Body scores to take them down. In Villains and Vigilantes, you whittle away Hit Points and Power. But in Mutants and Masterminds, the target of an attack makes a damage save. Blow the save enough and it's a KO, blow it a little and it's a bruise that penalizes further saves. It's kind of cool. It's got a good beat. I can dance to it.
You also don't buy up disadvantages in Mutants and Masterminds. You list complications and get benefits if and only if the GM actually uses them in the game. I like that a lot.
I still like Champions and still play it from time to time, but I've found that Mutants and Masterminds fits my desire for a Superhero game better. And with the DC Adventures license, there are a couple of sourcebooks (one out, one coming) that will cover a lot of builds for DC characters. So for players who aren't sure how to stat out a power, there will be LOTS of good examples.
