Delhi, the capital city makes it a lot of difference when you compare life in different IITs. The city where you live definitely matters a lot as you are going to spend 4-5 years of your life there. IITD is a cool choice if you want to prepare for IAS, CAT or other exams as the best coaching of Delhi are located close to the campus. Internet usage restricted to 500MB/week. In terms of placements, its electrical department is considered to be the best electrical department all over India.
Bombay, the city of glamour is one of the best place to live. The campus is a bit far away from the main areas which are connected via bombay local, but anyways Powai is a very beautiful place and the campus is very green and beautiful. Placements for CS department are best in India.
IIT Kanpur is the best place to go if you are interested to go for research related career. There is lot to study. Its a paradise for those having a genuine interest in pure sciences. IIT Kanpur was the first institute in India to offer Computer Science education.
Eventhough Kharagpur as a city is not that happening as the others, IIT KGP is the largest of all IITs in terms of area (more than 2000 acres...!!!!). In terms of number of courses, IIT Kharagpur offers the highest number of courses amongst all the IITs. It has Asia's largest technical library. THere are no strict attendence policies. There is unlimited internet access in hostels.
If you want to make a career in space science, IITm is the place to go. In terms of life in Madras, the proximity of the Besant Nagar Beach and Marina Beach make a nice getaway possible anytime. Also, being a part of the city, its easy to go out of the campus to the malls and theatres on short notice with little planning. Their fest Shaastra is the first student managed event in d world to get a quality management system n earn iso certification. Internet timing restricted to 2am :(
It is the oldest engineering college eshtablished in Asia. The best IIT for civil engineering. It has the largest library in India after the parliamentary library. On 3 April 2011, IT-Roorkee campus has been inaugurated in Greater Noida which is going to give a huge boost to the placements :)
A very beatiful campus (the greenest IIT) and large hostels providing single occupancy rooms to all students gives a perfect atmosphere to study. The cool climate adds on to the comfort of the students. Considered to be the best choice if Biotech is your dream career.