The eight classes on Indian trains...

There are no fewer than eight classes of accommodation on Indian trains. These are the classes, in roughly descending order of cost:

• Air-conditioned first class (AC1)
• Air-conditioned 2-tier (AC2)
• Air-conditioned 3-tier (AC3)
• First class
• AC Executive chair class
• AC Chair class
• Sleeper Class (Pictures)
• Unreserved 2nd class

I use to travel in sleeper class, the 7th one ;o) The main reasons: the cost, the total absence of other foreigners and the fact that AC makes me cold/sick. I like mixing with people. Sleeper is sometimes completely over-crowded and some passengers end up sleeping on the floor. My record: 15 people for 8 seats.

If you decide to go for such class make sure you don’t forget your blanket and locks. I would also recommend you to ask for an upper seat. You can keep sleeping even when others are awake. Might be useful when you have a long journey or/and when you boarded in the middle of the night.

Source

Check here for the railway timetable.