It is nearby the biggest railroad and bus station and not as safe as Barrio Norte & Recoleta. I've heard about several tourist robbed at Plaza San Martin (not in a violent way, but by distraction). I would not recommend to cross to Bus Terminal after dark.
It is is one of the nicest, oldest areas in town. It really depends on what your cross street with Juncal is. Suipacha?... Todo Bien. Esmeralda?... Pretty nice. The next street down, not great, not bad. But getting close to bad.
It really is that basic. There is a police station 1.5 blocks from Suipacha & Juncal ON Suipacha. There are art galleries galore in that neighborhood and the last Friday of every month from April to November, there is an "Open House night" (Noche de las Galerias) that is nice and there is champagne everywhere. There are nice cafes on Suipacha and some ok places on Esmeralda. There is a DISCO on Esmeralda b/n Arroyo & Av. del Libertador that is one of the nicer ones in town...
The area is really nice. But if you have your head in your ass and you walk through a park in the middle of the night, you might get robbed.
Really, it just depends on how far up your ass your head is.
Again it is an area popular with tourists, and also the theives that prey on them are there.
But I would agree it is a wonderful in summer, you will see people lying all over the grass enjoying the sun.
There are plenty of galeries and you are very close to the shops and lots of restaurants.
So I would say as long as you are aware you should be OK there.
How old are you? How "peaceful" do you want your neighborhood to be?
Although close to some bars and not far from Recoleta or mass transit, there isn't much to do at night within a couple of blocks of your apartment. You're kind of on an edge of the city there (not as bad as Puerto Madero) and you have to travel a bit to get to something.
Either going to the other side of Plz San Martin and then working your way to the Irish Bars on Reconquista or crossing Av. 9 de Julio to get to Jack the Ripper or El Alamo is the closest you're going to get to a "neighborhood bar"... unless you can afford hanging out in the bar at the FOUR SEASONS.
It's nice, because it's quiet. But it's quiet because it's dead.
I was mugged in Plaza San Martin, but looking back I can see why it happened. Generally don't stand anywhere for extended periods of time and just be aware. Most crimes seem to be those of opportunity, so try not to make yourself vulnerable.
Just a side note to those who say ´it depends how far up your ass your head is´. Anybody can get robbed, anywhere, and in ANY neighborhood. I am one of the most aware people out there, but I´ve had some bad luck, and have gotten mugged twice here - both times in Palermo, during the day. That´s why I say it´s bad luck, and my advice is to live wherever you like, given its not, you know, extremely dangerous, because most places aren´t as dangerous as paranoid foreigners make them out to be. Especially considering that you can and DO get robbed in Palermo and Recoleta, too!
Now, my advice is also to never, never carry a lot of valueable stuff on you unless absolutely necessary, and that way you reduce the risk of losing something very important. A money belt, or even just your socks or bra, is a good place for 100 peso bills. Don´t foolishly carry your passport around. Be prepared to buy at least one replacement cell phone if you plan on living here for many years (the statistics just arent favorable!) All that said, enjoy your area and enjoy your time! Getting robbed is unfortunate, but also unfortunately it´s a reality here and almost impossible to prevent 100%, unless you are extremely rich and can afford to go everywhere by taxi all the time (which isn´t even 100% safe, as we all know).