I'm both Airtel & DishTV user in HD connection.
Been using DishTV since past 3 years and Airtel since 9 years. Still faced no major problems, also service guys (on social media) are helpful.
Difference between Airtel & DishTV is UI.
Both's remote control sometimes slow to respond to TV. I got Full HD 1080p LED TV. Picture quality is sharper (sometimes oversharpen) on DishTV, but Airtel’s is natural. The audio quality is clearer in Airtel.
If you go for airtel, beware of customer care phone calls, as they'll tell you “as a valuable customer, you're getting this *channel* for one month” but the thing they WON'T tell is it's NOT FOR FREE! so don't share the OTP if they ask.
I was a Tata Sky user, used since 2008 to 2010. And my feedback is NEVER EVER DO THE MISTAKE to get Tata Sky. Also horrible no signal problem, poor customer service, etc.
I hope I've given answer to your question.