The best AC is with the lowest star rating .
Reason - The fins are too close and optimised in the latest AC and higher star catageory and those micro gaps accumulate a lot of dust which makes it too hard to service them . The indoor has to be completely disassembled and water washed under pressure to clean the fins . If not done , then the AC does not cool properly and leads to frosting . Micro gap fins are a no for a hot , humid and dusty country like ours .
Invertors are a no -no . Board failures and costly repairs . Unless you get an extended warranty do not even touch them .
1 ton is a generic term .. Check the power consumption for the AC which you choose . Since you are in Chennai check for an AC which has a tropical compressor which can cool with outside temperatures of 45C .
Buying the cheapest AC of the lot is the best . Always buy a little higher capacity to cool faster and for the outdoor unit to have more time to restart thereby saving a bit of electricity .
The best AC for me is the cheapest that I have which is a Camipro and it is virtually maintenance free . I have not even serviced the indoor for over 3 years and there is no dust accumulation in the indoor unit and it works the way it is supposed to . There are many HVAC dealers who have the Camipro and the pricing is excellent . Showrooms do not sell Camipro AC only industrial HVAC dealers do . Camipro is supposed to be Carrier low end . You can try these guys from whom I bought
http://www.rishabhenterprises.in/
Have no connection or affiliation with them . My extended family and friends have bought the Camipro 1 ton and 1.5 ton and we have no issues what so ever . The 1 ton costs about 20k and 1.5 ton cost us about 24 k . Probably they are costlier by a few thousands now .
ps- The indoor is very silent