i think the best berth in sleeper coach is the upper berth. I always prefer it. Its pros/cons according to me are:-
pros :-
1. sleep whenever you want.
2. least disturbances except for the lights.
3....
more... good berth length for above average height.
4. fans are located near your face.
5. no waitlisted passenger sits on your berth while you are sleeping which i have seen with lower and side lower berths and sometimes even with side upper berths.
6. easy to get while booking as families don't prefer it.
cons :-
1. bad for rail fanning.
2. during summers its a bit hot as compared to seats near window.
3. bad for keeping an eye on your luggage which is normally put under the lower berth unless you sleep with your luggage.
4. bad for people who fear heights and those who find it difficult to climb on the upper berth.
your thoughts rail fans.