Buddy, In my personal experience with 42 inch sony full HD
I recently moved from airtel to tatasky. Below is my experience.
1) Airtel HD quality is sharper and better than tatasky.
2) Tatasky SD quality is far better than Airtel.
3) Airtel is cheap to view all HD channels, Option is there to add single addon (HD Plus add on) to view all HD channels @ 204. Hence you can view all Tamil channels and all HD channels @ 171+tax+204. But in the case of Tatasky you can view all tamil channels @ 99+41, but for HD channels you don't have addon that consist of all HD channels. You need to opt for higher pack and also need to pay bullsh*t HD access Fee of 175 which is more costly. Better you stick with Airtel for good HD experience.
(All HD means it doesn't include premiere HD channels)