Some of the things that you should consider are:
Faculty time after the session in case you wish to solve your doubts. Many places, faculties do not encourage doubt solving.
Ratio of student to faculty and student to machine. More students in a class would mean less attention.
Facilities such as library, additional machine time. If you do not have a machine at home, or if you want to refer to additional material, it will help.
A good access to Net. Most of the institutes just run using a dial up line, even when they can afford a cablenet connection or a better connection like ISDN.
Instead of believing the sales talk, talk to existing students and get their feedback.
Placement Facility and also check minimum requirements. I know institutes, who offer facilities such as placement only if you are a graduate, doing a course of more than a year, and below a certain age.
Study Material. Check the study material offered by the institute. if you are paying your fees, you should not get photocopies.. but the originals in good condition. Also get the content checked by someone who knows the stuff.
If possible, check how the sessions are conducted, the cleanliness, cooling etc, if they matter to you.