Ive lived in san telmo for over 4 years. Originally, i liked the central location and the historic feel to it. since then, month by month, its increased tremendously in popularity. i can walk you around, saying, that used to be this, that used to be that, thats new, this just opened 3 weeks ago. lots of changes. its within walking distance to puerto madero and the nature reserve which i go to often.
One caveat about san telmo is it has many busses. every parrallel street is bus after bus. i cant make it out the door without a bus going by, and not to the corner without maybe 3 others going by. why is this a problem?? well, youll see when you get here. the public busses roar like airplanes (i was shaken up at 530 am this morning, it sounded like an airplane taking off with something wrong with its engine). down at street level, its ear piercing. streets are choked with black clouds larger than the bus itself. i cant even explain how that much can come out and so fast. The argentines just push the baby carriage through the massive cloud like its not even there.
The city (and ever city in argentina ive visited) lets them get away with it, no control at all. the busses roar, and spray clouds of thick smoke. I dont think a lifetime is enough time to get used to living like that.
Another caveat, is that its very dirty. dog poop is worse than other areas (cleaning up after your dog is very uncommon, many dogs even roam loose) and garbage is thrown everywhere, youll see people just swaggering down the street tossing away, then spitting.
But then again, you will find this in every part of argentina. Theres no part of the city, not even a park, that isnt littered. After you visit enough parks in argentina, youll actually think plastic bags DO grow on trees. I was at the san telmo park today, parque lezama, over 100 ferral cats. Very common in argentina. the botantical gardens in upscale palermo must have over 500, closer to 1000 of the ferral fleabags.
To sum up: San telmo, trendy but dirty and bus noise all day long with pollution youve never even thought possible. Recoleta, well theres a big cemetery, more expensive and no subway close by, and less dirty (but still dirty). Several busses from ST also pass through recolleta. One difference is they dont pass every street there so you can get away from it. Yet, if you walk on Ave. las heras, your eyes will water from the fumes.