If you can go to a CTI school that has ATC as a minor or an easy dual major where you get some other kind of aviation related education as a back up plan, that's a good idea. If not, then an associate degree is a good idea because you can get it over with cheaply and then transfer your credits to get something else as a bachelors. With the newest legislation, CTI does get a leg up again as long as you do well on the ATSA.
MTSU offers ATC as a minor.
Other schools offer associates.
There are 37 "approved CTI" schools, so call around and see what they offer and for what price. To be honest, you'll learn everything at the Academy, so if you want to do CTI for the hiring process, just do the cheapest, easiest, quickest option. The only guy in my class that didn't pass went to Beaver, the #1 and #2 people in the class went to MTSU, and everyone in between was a mix of military, CTI, and OTS. So just because it might help you get in (currently; the laws change constantly with this stuff) don't expect it to give you a guaranteed chance at passing the Academy.