I am regular user of Internet on move and I have tested Reliance data card in 2008 for 4 Month, Tata Indicom Data card for 3 Month. The main problem is they promise too much via ads and other thing and once you buy something you will never see the face of person who sold you data card. So finally, I switch to BSNL NIC Card which is at nominal price of 2850 Rs. And unlimited download at 250 rs/month and no problem at all from last 8 month.
The best thing I like about BSNL NIC Card is BSNL JTO told me that you will get 10-15 KBPS Download speed and I always get it. While relieance and TATA promised me 144 kbps speed and I never get speed more than 10 kbms while average speed is 4 kbps that really.