Which USB MODEM TATA - RELIANCE - AIRTEL is GOOD??

I am using an Airtel USB modem for the last six months or so. It worked fine for first three months, but then onwards, a lot of trouble has started. It often does not connect (even when the signal is strong enough) and even if it does, disconnects quickly (within 3 to 4 minutes. Then the software crashes, and the only way to re-activate it is to re-insert the modem). The services are atrocious. The call center washed their hands off saying that I should take it to an "airtel center where they can service it". After complaining to higher authorities, I did get calls from service personnel, but they never followed up and right now, it remains unusable for last one week straight.