Since DG seems to have already taken good care

of u folks here by answering all ur querries, I'll address only one aspect which would be troubling people blessed :)enough to choose from C/A/B. Have already Rx quite a few querries on this. while choosing from C/A/B or for that matter any B-School you might want to consider following things:
1)
Faculty Base: Trust me you wont find them any better than these 3 places. While C is known for its God-level

fin and Eco profs, a little use of google will throw up names Leena Chatterjee and likes.
2)
Alumni Network: B-schools are a wonderful ground for networking. Alumni network plays a big role in defining the type of companies which visit the campus consistently 'n also new ones. Check out the Alumni base in different companies
3)
Number of electives on offer: They define whats on ur platter to choose from. IIMC has been fav destination of people over the years for this reason too.
4)
Extra-curricular life: Since u wont be studying 24*7

and would need avenues for renewal, this is important aspect. Refer to the respective Life @ IIMx threads and also repective websites for more info on this.
5)
Facilities on Campus: quality 
of Internet connectivity, strength of library being some of the imp things. btw IIMC has one of the oldest library of this country with extensive collection.

other not so important

factors for some could be a swimming pool, football outfield, Gymnasium et al.
6)
Placement trends over the years: Believe i need not elaborate on the importance of this and many of the well read people on this forum would know the facts. for the ones still looking for details, placement info on respective B-School's website and news chips from MArch should be useful.:)
7)
Campus life: I'll personally pay more importance to this than the city since any B-schooler will tell thats where he is during 90%+ time of 2 yrs!
So nothing like the stress busting serene lakes of IIMC

. The kind of Camaraderie between PGP2s & PGP1s is something which defines the kind of good time u have on campus. Right from gyans during ur placements, to those tutorials before the all imp exams, to just a pep talk in the corridor when u stressed out is something which can only be expereinced!
YOur intentions of Specialization: This is also one of the important deciding factors. Though IIMC has been known for those heavenly Fin jobs & its Strong Systems background, a Marketing focused guy like me would tell you that oppotunites are just as good in Opern & Mkg :). Finding strenghts of A & B should be easy for u

9)
Brand Equity in Corporates Circle: While the things for people outside would appear different at times, a little chat with the Corporate honchos should be insightful.

10)
Pedagogy: this is important since it would decide how u learn over the next 2 yrs, how much time u get to THINK as DG mentioned.
11)
City: While Bangalore is known for its climate and "kool" place for youngsters, Ahmedabad for the mouth watering delicacies, Kolkata is known not just for the history attached (after all good Ol' britishers had reasons to choose their Capital) but also for contributions to education. Guess that explains the quality of profs in the land of Tagore 'n Amrtya sen.:)
Did i forget to mention Rossogullas?

Am sure DG 'n others would add to this list whatever i might have missed out.

and this list is in NO particular order of importance.
Am sure u will speak to lot of people before making the all important decision of ur career; and u'll also realise that there is very little to choose from these 3!
in the end the "small" factors like where ur girlfriend is might pull u to one of these 3 (someone reading this??) :neutral:
Any of the IIMC guys around would be more than happy to help in whatever manner they can. So get in touch.
All the BEST for a great life ahead..............!