If you watch only HD channels and you have a home theater, you should go with Airtel as you will get very cheap HD add-on options. However, if you want to watch most of the SD+HD channels and don't have a home theater, Sun Direct would be a better choice as their packaging is very good for SD in base packs. See below.
Airtel Pros:
1. Excellent HD Packs at affordable cost
2. Top class PQ and AQ in HD Channels
Airtel Cons:
1. Customer care is dumb about packaging and channels addition. Tech support is good though
2. SD channel PQ is average
3. Packaging for SD channels is not that great compared to Sun
Sun Direct Pros:
1. Excellent Packaging for SD+HD requirement at affordable cost
2. Top class PQ with HEVC technology (1st in India)
Sun Direct Cons:
1. AQ is poor on HD channels, you can't use it if you have a HT
2. Zero technical knowledge for the Customer care executives
Thanks that's really precise set of information, Yes i don't have HT however the only reason opting for SD is because of News and Kids channels as not all of them bundled in HD format.