I have been using BSNL for over two years now..... No major problems so far.....
Just the occasional problem or two with DNS or so....
Otherwise more than happy.....

Never even thought of Asianet or any other ISP.

Asianet may be good at solving your problems fast, but their plans are very stingy....

If you are a heavy downloader, go for 600 Combo... The best plan available with any ISP in India (to my knowledge).