You will probably hear this a lot, it is your personal preference. Which it is. I have a BOB, my girlfriend has Panniers. I took the BOB to Mexico and it was great, you hardly know it is there, until you hit about 40km/hr, then it is a bit unstable. I once carried 20L of water on the BOB in Mexico, on top of all my gear, and it was heavier, but not really that noticeable. The BOB on the plane was great, I took off the wheel, and the part that connects to the bike, put my bag in it, zap strapped the bungee cords and I was good to go on the plane. The BOB is great around the city as well when you want to carry a big load, like lumber or a lot of beer.

If you are going to be jumping onto trains a lot, dealing with a lot of traffic (downtown Delhi traffic) I would definitely go with Panniers, the extra length on the back is kind of a pain, and could be safety problem (drivers don't expect you to be that long).

The bottom line, the BOB pulls great, and if you keep it under 40km/hr, stay away from crazy downtown centres, you can carry way more stuff then with panniers, and if you are really crazy, you can put a rear rack on your bike and take the kitchen sink with you as well.