Your question makes no sense. What do you mean with "free DNS"? Free DNS Service - irrelevant for trading. Free DNS Server - irrelevant for trading. At the end of the day use your providers standard DNS if you dont know what you are doing there (which it looks like) or install a DNS server as per your OS package (windows has one on the servers) or just point your own server to googles anycast based DNS service. Again, it wont make a real difference, though.
OpenDNS, hands down. But, DNS 'speed' only matters when you make the initial connection to your data provider / broker. After that, the route to that site is cached and the 'speed' of the DNS server becomes irrelevant. In other words the 'speed' of your DNS server won't lead to faster trade executions or data feeds to you because the connection, for want of a better term, is 'persistent.'