In my opinion, most fighters still specialize in an area. Their ultimate goal is to become well rounded, but they still need to have a place they can go to, that can win them the fight. My personal opinion, is that you should consider doing BJJ to help compliment your wrestling. Become a great ground fighter, THEN pick up MMA later, and become well rounded. That way, when you compete, your goal will be to take the fight to the ground, and win that way. If you do it now, you'll probably just be a generalist.
That's just my opinion.
I would take MMA first
I trained with the Gracies in BJJ and it was taught as an MMA sport. Sure grappling was a large percent of the lessons, but striking and defense to striking was also taught and, if a student wanted it, leg strikes were also included. I guess I am biased towards BJJ, but if the MMA class also incorporates it into your lessons, then it sounds pretty well rounded. Flip a coin a guess (but if it was me flipping, I would be hoping BJJ won)
I'm off to college as a freshman in a few weeks and I really want to be learning and training and competing in BJJ. This school has two classes, MMA or BJJ, so I'm positive that they have a great grappling background. I considered MMA because I want to learn how to strike if a fight on the streets stay standing up. I don't know to strike at all. I have a wrestling background from high school wrestling. And I'm still going to compete in college. But also I could work my way around and do either a BJJ class or MMA class. During my time in college I hope to get a blue belt and probably short after college a purple then continue on from there. Since MMA features BJJ, is it best to get a bit of knowledge in BJJ before doing MMA?