I did a lot of research on various sites before I got thoroughly confused and just went with the costliest option i.e. Hitachi. I am not sure if Hitachi really would live up to the price expectations.
I bought Hitachi Quad TM 1.5 and it started giving problems in firt month itself. It creates a vibrating noice during compressor statup and shutdown and shakes the whole window, it wakes me up at least 2-3 time at night.
I am not sure why this can not be fixed by Hitachi. What came as a bigger shock to me was that the AC stopped cooling, I have used O General, LG, Onida, Assembled but none of these ACs gave me any problems in first three years,  and Hitachi was the most expensive one stopped cooling in just 4 weeks. The service center engineer told me that this might happen in 1 out of 100 ACs, it was a manufacturing defect of Gas leakage.
I actually bought an Onida after I bought Hitachi, and here is why I took this decision -
How much time would your AC run in a season, if its less than 3 months and one an average 5-6 hours a day, you may not really care too much about Energy Efficiency, what big deal if you are able to save 1000-1500 Rupees in a season, You would be paying arond 7-8 K extra for Hitachi/OGgeneral. But yes if you are a nature friendly person, go for a AC with an Energy efficiency of more than 10.
Mositure control - Do you really live in a highly humid environment ? If not, whats the worth. Infact, I would not want my AC to suck the entire humidity of my room and leave us with dry skiin and eyes next morning.
Cooling - This is an important point and most of us buy expensive ACs because of cooling capacity and effectiveness. Let me accept here that I am not a technical person, but these are the basic asumptions and criteriaes that I considered -
a) If your room is smaller than the recommended size for the specified power of AC, (e.g. if 1.5 tonne AC is appropriate for x square feet room and your room is less than that), than you would not worry to much about cooling capacity because all the ACs would be equally effective (with minor variations). The difference between a good AC and not so good AC would be the time it takes to cool the room and hence save power, but both will cool the room ith equal efficiency
b) If our room is slightly larger than the recommended size, then go for the AC with best cooling capacity and Energy efficiency.
- Service - I have used Hitachi service once, I think they are trying to do their best. I logged  a complaint which was attended the same day (though I had to call up the service center a few times) and my faulty unit was replaced in 4 working days. I would call it as a decent after sales service. but LG, Onida would probably give much better service. may be becaue you may need it more often after a few years of operation. I found the Hitachi service guy more professional than an LG one. May be just a sheer chance.
 
Closing thoughts  -
If your AC starts leaking gas, your better get it replaced if it is under first year of warranty. Once this problem starts there is no end to this.
If you personally know someone who assembles AC, explore that option, get the best parts assembled at the lowest price, but you need to ensure that you get service from that assembler.
It doesnt matter which dealer you buy the AC from, service in directly given by service center. So go for the best price.