There is nothing wrong with traveling around India by train, They are reliable and offer a very cheap way to travel as well as being able to watch the countryside go by.
There are a multiple of different classes of train, some obvious like 1st & 2nd class but there others.
Sleeper can be air con or fan, can be 1st or 2nd class
Seats air con or fan, 1st & 2nd class
The above can be booked in advance.
Unreserved fan -
There is nothing wrong with traveli