always try to use mtnl dns servers when possible. like 59.179.243.70 or 203.94.243.70 or 203.94.227.70using opendns is a bad idea because it takes 10 times longer to work. if mtnl dns sitting next to you in your city takes 18-19 milli seconds then opendns takes 270-280 ms for the same website because your website name goes all the way to usa for getting translated into the websites IP address.so unless you are using some website which is not in the above 3 dns addresses of mtnl only and only then go for non mtnl dns addresses. and once ure work is over switch back to mtnl dns.test for dns speed simply ping mtnl dns server and opendns server you will see the figures i have given above.Note: you can also use DNS servers of other ISPs physically located in near your home if some website is not working. but dont go for international dns servers they will be much farther away physically so much slower. also if u want you can make your own dns server, buts for more advanced users who need to host a website on their computer... so stick with those dns servers which are located physically as close as possible to your area of residence.