here's my take on each of the arts, BJJ, MT, wrestling and boxing.
BJJ
good for sports fighting, because of the reasons outlined above. it can get you VERY fit as mostly all BJJ practitioners are excellent athletes. useful ground tactics and sometimes even in a standing fight it can be good to know the types of chokes and holds they teach. but u don't want this as a primary fighting style when street fighting. only as something to support ur skills on the side.
muay thai
one of the best striking styles. a lot of power, and will get u really fit and conditioned. the punching may be slightly weak, but u learn elbows, knees, and kicks very well. it's also good cuz u'll learn to fight in a clinch which can be useful for practical fighting. but again, this is a ring sport 99% of the times. if u want to learn practical street fighting, this can be definitely useful but there are better ways. remember, there is no honour on the streets.
wrestling
very good for learning takedowns and how to gain an advantageous position on the ground. there is a lack of finishing maneuvers tho. i've seen a grappling match between a BJJ guy and a wrestling guy at my martial arts club, and the wrestling guy took him down and had him pinned. the BJJ guy went straight into a guard. the wrestling guy had no idea how to finish him off. again it's very good for sport, for getting fit and conditioned, and some useful grappling skills, but nothing beyond that if u really wanna learn how to fight. something to complement ur skills, not to be ur primary style... unless of course u love wrestling in which case go all out. same goes for anything else here.
boxing
teaches u great punching, movement, footwork, and etc. but the problem is u only learn punching skills. a boxer is a boxer, not a fighter. an average kickboxer could easily take out a good boxer... altho a good kickboxer would lose to an average boxer in a boxing match. again, something to complement ur overall techniques but not to be the one and only main thing.
if u wanna be an average sport fighter, go to that place and take a buncha things at once.
if u wanna be really good, i suggest u go to specialized schools where they only teach BJJ or only teach MT or etc., and get good at each individually and branch out from there. most MMA places that teach all those things at once, don't ever teach properly. it's more like a fitness gym that teaches u a few tricks and u get to have a protein shake afterwards... not good for beginners.
if u wanna be a good fighter on the streets, u can still go with this but i suggest u take a look at different options.