There are a handful of Indian restaurant in Buenos Aires and we have tried them all. None is authentic, the spices are mild and the dishes are not hot. However, for the sake of the saying "when life gives you lemon..." this is my ranking:
1 - Mumbai (Honduras 5684, C1414 CABA)
Cheap, extremely disorganized and slow service. But I love their parantha, which is flaky and hot.
They have a bunch of websites, facebook pages, instagram pages and two Google restaurants in the same location. It seems someone is very bad at password management and keep creating online profiles. Once you order from them directly on Whatsapp, you are on their list and they send you the updated menu and promotions by whatsapp. But only when they remember to. They also attach the menu with the prices not updated, and then they ask to pay a different rate. Again, extremely disorganized but the food is the best there is in Buenos Aires.
2 - Delhi Mahal (Av. Córdoba 1147, C1055 AAB, Buenos Aires)
Lunch special are cheap and you can stuff yourself on a budget. Not very different from Mumbai overall, but the food is milder. I have never tried to ask to spice up the food, to be honest, but they could have asked if I wanted my food spicy or not.
3 - Taj Mahal Cocina de la India (Nicaragua 4345, C1414 CABA)
This one is on the fancy side. The restaurant is big and well decorated. The food is not cheap but average in taste.
4 - Thali (José A. Cabrera 4175, C1186 CABA)
It is a closed door restaurant inside of Güngur, Indian Fine Arts. It is sort of a private cultural center on India where they give classes of Indian dance and host exhibitions of Indian-related arts. They also organize events with Indian dances and dinner nights. Since it is a closed door restaurant, you have to book in advance. The best part is that they don't do the usual stuff found at other restaurants, but I don't recall the food as being memorable. Call over the phone as they are not very responsive when contacted in writing.
5 - Delhi Masala Indian Restaurant (Defensa 714, C1065 CABA)
Probably the oldest Indian restaurant in Buenos Aires. We went there once, and it was the same stuff as in Delhi Mahal. We need to revisit, but the distance and the dull memory haven't yet prompted us to drive 'til there.
6 - Dostana (Humboldt 1721, C1414CTQ CABA)
Not particularly cheap, not particularly tasty and just two blocks from Mumbai. However, the service is quick and nice. Been there once, and that's more than enough for me.
7 - Ali Indian Restaurant (Av. Sta Fe 2784, B1640IGO San Isidro, Provincia de Buenos Aires)
It is the only Indian restaurant outside of Capital and it is tasteless. The ambience is depressing and the prices weren't cheap. They do have themed nights with all-you-can-eat which makes it a popular option in the area. Both times I went I wasn't impressed with the food, the price nor the ambience.
8 - Tandoor (Laprida 1293, C1425EKE CABA)
In the fancy neighborhood of Recoleta, with dim lights, Argentinian waiters dressed like indians and a very upscale attitude and a hostess welcoming guests at the door. It was crowded with foreigners and affluent locals. However, the food was tasteless, spiceless and the waiter didn't ask why we left the food in the plate. I emailed them on the next day to complain. I was thanked for the message and promised they will check it with the kitchen. Which means that they didn't do anything and never got back at me. I wasn't expecting a free meal, but they could have made the gesture and offer to come back and get a discount. They did not. Which is unfortunately too common in Buenos Aires, but still disappointing coming from the fanciest Indian place in town. And they screwed my 40th birthday dinner, so I am quite bitter about it.
Add that it was also the most expensive of the (short) list above... a well deserved last place, I am sorry.