As you have not specficied your upper limits, I take liberty to put options for you , as per my view. It depends on your pocket what you can afford to pay.
what are your choices.
If you like to have comfortable peaceful journey, it comes at a cost, and thata is AC1st class.
If you like to have economy with comforts 2AC/3AC...
more... is preferrable.
If you like to travel sitting only n comforts travel in CC ex class.
If you like to have economy only then, SL is preferrable.
If you like to have THE ECONOMY and also desire to have intimate look into Indian Train Travels, go for unreserved second class.