Since my handle gives away my barrio, I've been trying to stay out of this discussion. For some reason, expats in Buenos Aires seem to have even stronger feelings about their city's barrios than, say, New Yorkers. The fact is that I agree with almost everything that's been posted here - both pro and con regarding San Telmo.
When I was looking to buy an apartment some years ago and first met with a real estate agent to discuss possibilities, she asked about San Telmo. She mentioned its handsome buildings, said it was up-and-coming but that there were still good values there, etc. I replied that if I were 25 and spoke perfect castellano, I would be looking for a little house or PH there. But I'm not. And I don't. So let's not bother.
I've always loved the architecture, the amazing antique shops around Defensa, and the traditional bars that line San Telmo's main streets. I find myself increasingly attracted to the destination restaurants, bars, galleries, and theaters in the area. On the other hand, I avoid the weekend street fair like the plague, and I can't imagine confronting that every Sunday if I lived within a couple blocks of Defensa.
Don'tMindMe's post is accurate in describing the official limits of the barrio, which don't restrict what realtors call San Telmo. In my mind, I think of San Telmo as extending north to south from the Avda Belgrano to the highway, and west to east from Yrigoyen (aka 9 de Julio) to the Paseo Colón, although it's officially offset by a few blocks in each direction. "My" San Telmo seems more coherent to me in terms of architecture and neighborhood feel than the official barrio, which helps explain why realtors and people looking for places to live tend to use an expanded definition.
Whichever limits you accept, it is still a large area. Its handsome buildings from the late 19th and early 20th century fell out of favor long ago as the city's gentry moved north - to Retiro and the Barrio Norte/Recoleta and, eventually, on to Palermo and Belgrano and the Northern suburbs. The folks who had built San Telmo were replaced by working-class families, with many immigrants from poorer neighboring countries and eventually a good number of squatters. This profile is true for much of the neighboring zones as well - Barracas to the South, Constitution to the West, and Montserrat to the North.
It takes a long time to gentrify such a neighborhood, especially if you consider the similar adjacent barrios. By contrast, it took only about 10 years for Palermo Soho to turn into the gentrified zone - I might say overly gentrified - that it is today, in large part because the architecture was low-scale, mostly 1 or 2 storeys, and almost all commercial. (Into the 90s, it was mostly auto repair shops and small-scale factories.) A small property with a single owner can be easily acquired for renovation and alteration into trendy apartments, shops, bars, etc. Once a few properties convert and values start to increase, the remaining owners tend to jump on the bandwagon and reap their profits
San Telmo is different because each of the larger, older buildings that are prevalent there typically has separate owners for each of its apartments and offices and shops. If the majority of a building's owners can't afford basic maintenance and security for the building, only a true pioneer will be willing to invest in upgrading one of its units for modern living. And this work can be complicated in a multi-owner building with antiquated plumbing and electricity (and sometimes no reliable elevator). Once a building has a couple renovated apartments, however, the other units tend to change rather quickly as original owners cash-in their newly found profits by selling to less-pioneering yuppies. The changes then spread to neighboring buildings until the entire block has been upgraded.
This kind of change usually happens in a checkerboard pattern, building by building and block by block, which explains many of the earlier comments in this thread regarding "good" and "bad" blocks, streets, and sub-zones. There are good aspects to the slower pace of renewal, like the continuing feel of an original working neighborhood. And less attractive aspects that arise especially when "rich" folks begin to populate a less-affluent area, building "lavish" apartments, and bars and restaurants and galleries that are beyond the means of longtime residents, and especially of their kids.
Looping back to Marche Exile's original question, I don't think anyone can tell you whether San Telmo is a good neighborhood for you - you need to spend some time there and decide for yourself how the good and bad aspects measure according to your own needs and style of living. If you decide you want to be there, you'll also need to decide if the specific block and building in question are comfortable for you, by day and by night.
You mentioned a relocation company, so I assume you're planning to be here for at least a year or two. I strongly recommend that you tell them to find you a good furnished rental for a month or two, or PM me for recommendations. If they are relocating furniture and furnishings for you, you can count on nothing actually arriving at your home for a month or 6 weeks in any case. (If you're thinking of shipping things by air, PM me for a side discussion on why this is a bad idea.)
Should you be surprised by an early arrival, your relo company will store your major stuff for a few weeks at little or no cost. You can use your time in the temp apartment to explore the city's barrios and decide where you really want to be for the rest of your time here.
And where should the temp apartment be located? Play it safe and stick to Recoleta or Palermo while you get accustomed to the city. Both barrios are comfortable and convenient, and foreigners don't stand out. Getting started in the city, you will feel comfortable anywhere in the zone bounded by 9 de Julio, Libertador, Coronel Diaz, and Santa Fe. Also, any part of Palermo - especially the Palermo Botánico and Palermo Nuevo zones - will be comfortable for a starter home here.
