Mostly private dealers like Red Bus, Parveen Travels are good as per my opinion. They give really neat service for AC, non-AC and sleeper coaches and I mostly travel in sleeper coaches. The roads from Chennai to Tirupathi is really clear and smooth. Also the bus has television and the seats are fully cushion and semi sleeper seats, which is enough nice to sit and sleep and watch over windows. If you are travelling by bus, keep in mind that, buy some water bottles, chips or snacks items and have a happy journey.