All styles of dance are great, it just depends on what suits you best.
Personally, my favorite is hip hop. I love it because it's so much fun and there's no rules to it. Like in ballet you have to have your leg extended at the perfect degree and your toes must be pointed at all times...But in hip hop you can really just let loose and be yourself, show your true personality by adding some of your own attitude and variation to the moves. Plus hip hop really gives you strength in your upper body and core and you learn lots of cool tricks and isolations. It boosts your confidence and I really suggest it, especially if you're someone who likes to show off or you have a lot of energy.
Ballet is good for technique but it can be hard to master. I remember first learning I was so discouraged because I couldn't do anything, but slowly I got the hang of it and it really makes you feel beautiful and graceful (plus it helps with your balance and turns).
Jazz is a lot of fun, it's also one of my favorites. I highly suggest jazz because I see it as the main part of dance. If you ever want to be on a dance team for your school or audition for something, you need to be good at jazz. It's great for beginning dancers.
Tap usually requires you to be pretty quick on your feet. I don't currently take tap but I used to and I assist a younger kids tap class. It's personally not my favorite, but a lot of people love it so watch some tap videos and if you like it, then try it.
Those are the four basic styles of dance but there's many more to choose from (modern, lyrical, pointe, etc...). It really depends on where you want to go with dance. If you want to become a serious dancer then I suggest jazz and ballet as a start. If you just want to take a class or two for fun as an after school activity, then take hip hop, jazz, or tap. Look for some videos of different dancing styles of youtube to get an idea of what you like. Or you can go to your local dance studio and ask to watch some classes so you can choose. Good luck, and have fun dancing!