A colleague of mine wants to buy an AC too. From his research, I will suggest few things:
1. Don't buy AC from the "best" brand, rather the brand which have its Service center nearest to you.
2. Blue Star is a good brand which provides good value for money.
3. O General is among best brand, but again, refer point 1.
4. Buy Split AC only if you have prior experience with ACs. If not, better buy a Window AC.
5. Star ratings don't matter. Any AC with 3 or more star is good to go. Not much difference between a 3, 4 or 5 star rating ACs.
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You will get a 1 ton AC of Blue star or O General under 30k.