French is not a synonim of quality, but the best in my view is "Le Sud", located in hotel Sofitel in Recoleta. It's expensive (expect 700/800 pesos for two) but the new Chef is Olivier Falchi who was for ten years "the" Chef at La Bourgogne (mentionned by Katti).
He won numerous prizes including the one of the mejor Chef of all latin America (!).
Expect "grande cuisine" there, meaning that after tasting for 1 minute a plate, you still are discovering new flavors.
I mentionned to Perry the eventuality of organizing a BAexpat dinner there, maybe could a degustation dinner be organized with some wine for 250 pesos each (on a dead day for them maybe can something be organized?) ? Expensive but cheap in fact.
The best ones I've been to in the past six months or so are
Crizia -- Gorriti at about Thames
Fantastic menu, slow roasted cordero, oysters, fish, but the wine list is expensive. We went for our anniversary, be prepared to drop some cash but have a truly wonderful meal.
Chila - Puerto Madero
Haven't been since last sumer but everything was very fresh, presentation very nice, i seem to remember a good drinks list.
These are both expensive options (for those on pesos), as far as best restaurants for a lighter wallet I can give other recommends if you like.
Oh and it's definitely not La Cabrera. La Cabrera used to be a lot better in my opinion, now I think the quality/price ratio is way off, and it's just too flooded with tourists -- I think they've suffered the Guide Book curse -- every tourist has heard of them now so maybe they don't have to try so hard.
I liked the presentation that they used to have, but I think they've cut down on it -- all of the little ramekins (pots) of different sauces, potatoes, onions etc -- last time friends of ours went they said they didn't even get them -- is it something you have to ask for now?
Friends of ours are coming into town next week -- we'll probably end up taking them to El Mirasol for the Argentine parilla a la tourist experience. I will probably tell them to skip La Cabrera in favour of Crizia.
La vineria de Gualterio Bolivar is the best restaurant I've been to here BY FAR.
Its a set, 10 course menu with the option of buying wine by the bottle or having a desgustacion de vinos (a glass or half glass to share per course). Excellent ingredients, innovative preparation and a really low-key atmosphere where the emphasis is on the eating and not the dressing up, etc. Its not cheap (about 500 pesos for 2 people with wine) but a similar kind of dining experience in Europe/the US would set you back a fortune! I went for an anniversary and would highly recommend it to anyone... (phone in advance to request a vegetarian option).
The couple of other higher range places I've tried have been very disappointing...as have most of the mid-range places, although Yuki was good for Japanese food. I used to really like Katmandu but I like to get 4/5 plates of Indian food to share and that's just become too expensive to justify there.
I usually visit lower-priced restaurants: I like Sarkis, Las Cabras and (for veggies) los sabios (all you can eat place) - They're all usually packed out/cramped but the food knocks the socks off most higher-priced prices places here IMHO...