I was in Buenos Aires for 7 weeks - three in Palermo Viejo and four in Gustavo's apartment in Recoleta. I really enjoyed PV and was sad to move when the time came, but the sadness was short lived. I fell in love with Recoleta while I was there.
I am a single female, traveling alone, so it is important for me to be somewhere where I feel safe walking around. As much as I liked PV, I had some sketchy experiences there. I had nothing but wonderful experiences at Gustavo's place. PV is like Brooklyn, with designer shops and beautiful hipsters and is just hopping (and loud) all the time. Gustavo's neighborhood is mostly families and older people with dogs, young professionals and such. But I was really comfortable there. I was inspired by all of the active people in the neighborhood to take up running again and often ran after sundown in the nearby (beautiful!) park and felt completely safe doing so. (There are so many people getting their fitness on in the park, at all hours, it is a really lively place to be.)
The apartment is walking distance to the Cemetery and two really great museums. It's close to a good grocery store, a gluten free bakery (Cooking Time) in one direction and a gluten free cafe (Gout) in the other, and there is an excellent Juice/salad cafe (Be Juice) just a few blocks away. (I'm coeliac, so this was really important to me.)
I work online, so really lived in Gustavo's apartment like I would anywhere -- less like a tourist and more like someone who is beholden to a group of online co-workers for set hours during the day. So I can tell you that the internet works great and that the sun streams in through the windows there from 10 - 3, which is lovely when you're stuck at a desk.
There aren't a lot of restaurants (or bars) in the neighborhood, so if that's what you're looking for you would be happier in PV. But I mostly cooked at home, so that didn't bother me. The kitchen is small, but it's fully functional. And a maid comes once a week to do the heavy cleaning, which was a nice perk.
If you aren't coming to Buenos Aires to party, I definitely recommend Gustavo's place, especially for a long stay. He is also going to be renting the next door apartment soon. He walked me around it and I can recommend that place as well. It's beautiful. If, while you're there, you see some people opening the door next to you, say hi. They will be fellow travelers and you can share tips!