Nightclub two-step would be my dance of choice for a prom, no question about it. You can dance it to a wide range of tempos, and you can grow or shrink the steps more easily than many other dances depending on how much floor space you have. A prom is practically guaranteed to be full of the right kind of music for nightclub two-step. I found it easier to get a handle on at first than the other dances I'm learning, though of course that may just be me.
It's sometimes called California two-step, but don't confuse it with the various country/western two-steps, which are very different and probably wouldn't be as useful at your prom.
Around my area, all the ballroom dance studios teach it alongside the more traditional dances. It may be less common elsewhere but you should be able to find someone to teach you.
Here's an interview with the guy who invented it, if you want to find out more.