This should be like high school where they make you take a lot of subjects so, yes, you are somewhat conversant in them when you grow up, but also to discover a passion. Once you're reasonably solid in your seat and aids, do take some dressage lessons, some jumping lessons, some reining lessons, etc. and, most of all, see if you can handle a horse outside the confines of the arena. I do believe that the initial lessons in any discipline teach a lot of transferable skills, so your time is not wasted. It only gets crazy when people get addicted to winning. You also need to take into consideration your horse's preferences - what's boring for some is exciting and entertaining for others, what's exciting for some is scary and frightening for others.
In short: the only way to find out what you like is to experience it - then you'll know.