Over the last couple of campaigns I've run, I've started putting together a theory about player types, and the mix of them that works for me. It's inspired by the Robin Laws theory, which I snagged a bunch of names from, but I've focused in on the specific types that interest me, and tweaked a couple of the definitions.
First, there's instigators. I need at least one in a four or five person group, and if they're capable of working together it's okay to have two. These are the schemers, people who stir things up because they're going after their own fun. They crash weddings, assassinate NPCs, and generally keep the game going and energy high. They don't have to be off-the-wall wacky; the Duke Marlow Burrin in my current Traveller game is one, and he's a fairly low key personality, who just happens to keep himself busy directing the team and finding new jobs for them to do.
Then there's character actors. I like to have one or two of them in a game; they're not as vital as an instigator, but they also don't have quite the same destructive potentional. Not nearly as highly charged as instigators, they won't just run off and do things because they seem interesting; they need to have a reason to do things. Luckily, they tend to be pretty good at supplying those reasons, and give me a lot of material to throw interesting events at them. They also tend to provide a lot of fuel for instigators, providing events and ideas for instigators to plan around and interfere with. Sigrid Halstead was the main character actor in Is This Fair; she wasn't always coming up with crazy schemes, like Blank, but she acted as a foil for his antics, and her own dependable motivations drove the heart of the game.
Another important type are lurkers. These might have a touch of the character actor in them, and often give me long backstories, and come up with strange goals for their characters to work towards. But at the table, they're not nearly as active as the first two types -- they tend to go along with whatever the instigators or character actors have planned. If they do have their own goals, they tend to let the instigators in the party come up with avenues to attack them. This makes them vital as a glue for a party, and my best games have all had at least one.
Then, finally, there's power gamers. They're in it for the numbers. Easy to motivate, easy to please, and as long as they don't badger me about how they "should" be allowed to use this or that power combination, easy to manage. I don't consider them vital to a game, but I don't mind having a couple along for the ride; they often use the game system to come up with creative strategies, and if they get along with the instigators can provide valuable "jam partners."
The important thing about my ideal player mix is that it is a mix. I've had trouble with games that were all instigators; they tend to get into fights over who's mad scheme gets enacted first. A too-lurker heavy game would have obvious difficulties; too many character actors, and there's just too much material for me to completely incorporate into the game, if it doesn't turn into one big talk-fest where no one ever does anything. A power gamer heavy game could work, but I don't think it'd be all that interesting; that type is best in a support role.
But an instigator, a couple of character actors, a lurker, and a power gamer make for a great game. Just the right mix of random chaos, story-building motivation, and "there for the ride" resources. I don't know just how universal this combination is, but it's worked for me.