I think dabble in everything a bit at first to find what you really like, then pick one to be your main focus at first. put most of your effort initially to improving in the one game and mostly just play the others once in awhile as a break. If you are trying to learn too many games at once it'll really slow your progress down.
Also, you need to consider why you're playing. If it's for fun, sure play whatever. If you want to become more serious then, these days, that almost dictates that your game, or at least your main game, better be some variety of NLHE.
I mean its not gonna do you any good to specialize in, say 5CD, even if you love the game and can crush in it. There will be little to no opportunity to use this skill since almost no one plays that game anymore. There are a few other games like this to that, while fun, it'd be foolish to invest too much time in since so few people play them and you'll have difficulty even finding games sometimes, let alone making any serious money at them. Razz comes to mind..... Stud......PLO8....Triple Draw.....These are all games that are fun and I enjoy playing once in awhile, but these days, if your goal is to make any kind of serious money, they just aren't the best choice.