depends on ur place
as on paper EDGE is faster than CDMA which BSNL is offering but once again its on paper
at many places AirTel networkmay not have better EDGE support or too much DATA trafic which would give u slower speed and also EDGE / GRPS will come with one single IP for a total Network Area which means virtually u are getting a Static IP
so problem in sites like Rapidshare.com or same
in case of BSNL its cheaper in many case will come with better upload speed and dynamic IP but it will not support roaming and initial investment is high as with AirTel
u can use ur phone as modem but with BSNL u have to buy their DataCard
so where are u from ??