Tata sky is better, but be prepared for inferior signal quality in summer. The day time reception is bad or nil.
A stonger Philips LNB can solve the problem, but the last time I checked, Philips LNBs were not available in Doha.
I think Airtel Digital TV uses MPEG4 transmission technology. Have seen it in India its better than TataSKY. But I dont know of anyone who has Airtel TV in Doha.
But then everthing depends on INSAT4A's footprint which goes weaker due to sun outages during summer.