As bisonrav says, IngiGo is a LCC service but very punctual and reliable. Seats are rock hard though, and it gets tough even in an emergency exit seat (extra charge) between DEL and BOM.

Vistara is an excellent carrier - clearly with very large input from SIA (SQ) - you could call it control from Singapore. Good seats, very well trained and pleasant crew. I usually take the premium economy option if possible, and you get a small snack and drinks as part of the service.

Air India is Air India - trying to be full service but it’s really not. I’m not sure I have anything positive to say about them (although I’ve never flown them longhaul, where I understand they are getting better).

SpiceJet is much like IndiGo but less reliable (in my experience) and a bit more budget. I try to avoid where possible, if IndiGo or Vistara are an option. For more remote cities, sometimes you may not have a choice.

Overall, unless you are on trunk routes between the big cities in India, you may not have a choice (or very limited choice) of carrier so that makes the decision easier. Sometimes the schedules can be a little nuts, and I have seen a few occasions where one flight has been “preponed” on the day and merged with an earlier one - which is not good if your schedule did not allow for the earlier flight. All in all, the joys of travelling within India