I use 'A field Guide to the Birds of India' by Kazmierczak. It is best of the lot amongst affordable field guides for reasons well noted by Apana.
But like most field guides it has limitations. It is important to understand the limitations of a field guide.The variations in plumages, Calls and even distribution of birds can confuse and mislead one easily on the field.Nothing can substitute Field experience in the company of experts. I try to accompany some of the veterans on this side of kerala
on their field trips whenever i can. You get loads of info which you will not usually find in the guides. Especially interesting behavior and nesting patterns, Calls, Elaborations on ID features given in the Guides, Local names etc. Calls in particular unless you have a good audio, I had been taken for a ride by drangos on CSE calls atleast thrice.
Now i think i can more or less distinguish the two thanks to a local friend who is also a good bird guide. The point im trying to make is using a field guide when in company of field experts will make you realise its worth and also give you a lot more to add to the information you get in a field guide.
Regards
Roopak