Dont agree fully on all the Palermo, San Telmo pro and cons! I live myself in Recoleta, close to Palermo, which I really love....buuuuuuuut, around Recoleta and Barrio Norte there is nearly no cozy inexpensive bars and hang-outs! You have bars in Palermo of course, and I spend a lot time there....... but its very mainstream and posh.....all cafes look the same with their stupid feng-shui bamboo in the door and so on. On top of that, Palermo will be the first to fall of the cliff when crisis hit this country.......you already see the emptiness in many bars during weekdays. On contrary, San Telmo actually offers a lot of nice relaxed hang-outs, without beeing overpriced and posh. Of course this is due to the much lower rent that both tenants and commercial places pay. So my advise would be to go and check out for yourself some days. Good luck!
(Just realized I only talked about bars now......need to join AA!)