Welcome! lot's to learn and info is easy to find here!
It would depend on whether you prefer striking or grappling more, I've taken Judo and BJJ throughout my life, but you may prefer to mix in some kicks with your punches with some Muay Thai or Kickboxing classes.
Like Hit said though, wrestling is the safest rout to go if you haven't pursued it yet, as it usually teaches newcomers the basics of nutritional discipline, and weight cutting more than other fighting styles would. This is almost an essential step for an up and coming MMA fighter, and it is something that will likely make the difference in whether you win or lose your fights. So either you take it now, or take it later!