Lotsa good data above from folks with much more experience than I.
I have trained in a few different styles: Okinawan karate, Japanese Jui-Jitsu, old-school Army combatives, Brazilian JJ, and some kickboxing.
I learned a few things from that training and, well, getting older and more break-able my own self that don't seem to have been covered, yet.
1. Where are you in your life?
What is appropriate to train as an adolescent may not be something you can or want to do later in life. Some styles are more appropriate for the young, who can recover more quickly and who have the time on their hands.
2. How much are you willing to put into your training?
I liked the kickboxing training, but when two out of the three trainers I was working with had a speech impediment it dawned on me that I might be the one with the speech impediment in 10 years. I was not THAT into kickboxing to sacrifice the brain cells required to get very good at it. Sweat, pain, time...I am willing to shell that out. I'm not willing to get my head pounded that regularly. (OTOH, you really have to know how to take a strike and operate through it. Just don't make a habit of it, IMO.)
3. What are your goals?
Suggested above, but worth repeating.
4. How much baloney are you willing to put up with?
Most traditional MA have some cultural component: use of foreign counting systems, titles, names, etc. That is no big deal. But, some just go ga-ga and way overboard, IMO.
Non-traditional MA have their baloney components, too, that can get tiresome.
5. Enjoying your training can make up for other shortcomings in the particular style/circumstances.
Yes, you will have to put out effort, suck up pain, and all that. But, truly enjoying an art/style is worth a whole lot. Most importantly, if you enjoy it, you are likely to train more often. To run with some of the discussion above, if you enjoy boxing, but hate kickboxing, stick with plain ol' boxing for a good while. A skilled boxer is no chump, despite his lack of leg strike technique.