I should probably change them back to my ISP's (Vodafone Cable - which google seems to think should still be 126.96.36.199/188.8.131.52). CDNs and local caching and all that. I have had issues with Vodafone's DNS in the past though, so I wondered whether I should make one of Vodafone's DNS servers my primary, and then something like Google or OpenDNS my secondary.
I know where to change the DNS settings in my router, but that's about the extent of my knowledge of DNS. I've no idea when the primary and the secondary servers are actually used - based on the names I figure the secondary is used if the primary isn't available for any reason. So making a completely separate DNS server my secondary seems like a reasonable thing to do.
Or is that a bad idea for some reason?