All of the search engines above have secure (read that encrypted) SSL connections. Unless the provider turns the SSL key over to NSA, you can have a high degree of trust your search results are private. That is unless your PC itself is compromise somehow (e.g., keylogger, malware).
I currently have been using duckduckgo, and have used the other 2 you mentioned.
The last time I looked Ixquick was based in DC. That made me suspicious.
My local ISP has partnered with Google and I think they manage the local DNS server. If google owns the data I am not sure that the search engine I use makes any difference.