Kulty
, ideally you want to have one dedicated main that you can devote the majority of your time to and be confident with in tournaments (this will be your strongest character, and potentially of a higher tier than your other characters) and then one or two pockets that you can pull out for bad matchups.
The difference between a main and a pocket, as I see it, is that you don't play your pockets as standard. In a tournament setting or a similar competitive event, you want to play with the character you have the most experience with and can perform the best with: therefore you'd go with your main, and only take out your pocket if you struggle in a matchup with your main, or if you want to have fun and switch things up a bit.
The danger is when you try to "main" too many characters, because then you risk spreading yourself thin and won't have a strong character to rely on in a high-level competition. That doesn't mean you can't play multiple characters (diversity is, after all, the spice of life, and you will discover new things about how to play the game if you have experience with different playstyles), but you do want to have a good character that you know is your best and that you feel confident with. Try to find that character and stick with them, then experiment with others in your spare time in case you need help with certain opponents.
Now with that said, I think it's best if you keep that consistent between games, especially if you want to play more than one game seriously. If you want to play them to an equal degree, it may be best to just to just have one dedicated character in every game, but remember that it's going to require quite a bit of dedication to maintain that kind of balance between games; alternatively, if you want to play
Smash 4 as your "main" game and then play other games on the side, you're gonna be dedicating most of your time to
Smash 4 and the other games won't matter as much, so you don't really need to worry about counterpicks and pockets and things in the other games. I play
Smash 4 and
PM competitively, and I dabble in
Melee for fun, but I'm definitely more interested in
Smash 4 than
PM, so I devote most of my time to the former and only go in for the latter when I want a change of pace or I need to practice for a tournament.
Playing Ganondorf in
PM suits me fine because he's a character that doesn't require too much technical understanding and he's very fundamentals-based, so I can do well with him intuitively and not have to practice too often, and that means I have more time to practive
Smash 4 - you may want to try and find a character like that, a character that suits you and doesn't require too much maintenance to keep up to date with. The important thing is that you don't try to bite off more than you can chew and become inundated with too many different fighters to train with: if you don't need a secondary to cover bad matchups and you're just playing them for fun, consider not training so much with them and just dedicate yourself full-time to the character you do want to play with.