Tata Sky Advantages
The display and sound quality is too good ofcourse because its digital
Information(when u press I on the tata sky remote) - Gives you brief description about the programs/movie etc. This is really amazing feature.
The information about current running program, all the programs/shows/movies that will be played on that channel for 1-2 days. This is for all channels.
The channel guide is very helpful, basically the overall User interface is very good in Tata Sky as compared to Airtel and Reliance.
Tata Sky+ HD Advantages:
The power of Tata Sky+ is amazing, for just few bucks more, you will actually get awesome features.
Recording of series is the best options - and you can have recordings in 2 channels at same time too. Also the hard disk space is good, it will accomadate lots of serials.
The pause, fwd and rewind are really cool, you wont miss a thing in your programs this way
Also, the HD channels quality is great, and currentlly none of the HD channels have ads, so you can enjoy ad free movies/serials.
I think you should definately give a try at Tata Sky+ HD