Quimbombo is a stylish restaurant spread over 3 levels overlooking the fountain in Plaza Armenia. This area always has nightlife going and is popular with foreigners for a fun and modern take on Argentine culture, and Quimbombo is consistent with that. There's a yoga studio on the ground floor, so head up the stairs to find restaurant staff and be seated. We called ahead for a reservation and were rewarded with a table in front of the windows -- the combination of the nice view and warm, pretty candlelit interior made for a really nice atmosphere. It's romantic for couples and groups alike. On the top floor there were some outdoor areas as well. It looked like they could accommodate pretty large groups (~20+?) with advance notice.
It is definitely on the expensive side by local standards; for dinner for 4 without alcoholic drinks we spent 900 pesos, about $70 US, but saved 20% by using a credit card of a certain type (this sort of promotion is common at higher-end argentine restaurants). There is a 20 peso "cubierto", or per-person charge, and dishes ranged from 100-200 pesos ($8-15).
The menu is quite tempting, with a dozen cocktails, some juices and milkshake-type drinks (which come in pretty glasses) in addition to a pretty extensive wine list. About 1/2 the dishes on the menu are vegetarian with a handful of vegan; they have labels for veg*n/GF (celiac) but we noticed at least one wasn't marked correctly, but the waiter was helpful clarifying, asking the kitchen if he didn't know something. Unfortunately they said they were out of tofu the night we went but we still had a nice vegan meal, there just weren't a ton of food options to choose from. The vegan dishes we ordered: ginger-lime lemonade; "Almond Day" a drink made with almond milk, banana, cinnamon and vanilla; parrilla appetizer with "sausages" which were more like meaty crumbles wrapped in a housemade skin; Thai roll which was like a breaded spring roll with actual hot sauce! (sriracha?); vegetable wok with rice which was tasty. The best thing about the food here was that they didn't hold back in making each dish fully -- it was much more flavorful than typical Argentine food.
The service was a bit inattentive when we were waiting to order or for the check but the food came out at a good speed. With a relaxed attitude, we were able to have a fun meal that met our omni Argentine friends' as well as our standards.
Cons: Limited vegan selection, Expensive