You're going to get so many opinions asking about neighborhoods. San Telmo is the best neighborhood ever!!! (Me and everyone who lives in San Telmo, lol.) San Telmo is the worst, what a hole!!! (Everyone who lives in Palermo/rich neighborhoods.) If you do choose San Telmo, make sure it's actually San Telmo. That place on Salta...I would also say hell no. That is in Constitución. North of Independencia on that side of 9 de Julio is Monserrat. I lived there and liked it a lot, but once you get down to Independencia I don't think it's a good place for anyone to live, much less a newcomer. The vibe changes immediately. Over on the other side of 9 de Julio in San Telmo, I'd say you're good until avenida San Juan.
Why live alone as a study abroad student? You're European and porteños love Europeans for friendship and romance/sex--especially blonde ones--but even so, if I were you I'd look for a shared house in San Telmo proper. It will be fun and you'll have people to go out with. Lots of nightlife in and around San Telmo; share cabs to hit Palermo on the weekends and you won't miss anything. You'll also be walking distance to UCA, which believe me is preferable to a 45-minute bus journey every day coming from one of the neighborhoods your school recommended (that's with light traffic). My study abroad friends who went to UCA and lived in San Telmo had the time of their lives. They still talk about it.