You're right, we haven't taken a poll (nor have I seen one. Personally I feel like MSTest has been slightly more often used. My coworker feels that NUnit is slightly more popular. But both our feelings are purely subjective opinions. The two seem to be running neck and neck (if this were a race). I don't think you could go wrong with either one of them.
Moq (or any equivalent) is almost never talked about in our world though.
the Telerik team