On my last greenfield project I got to pick the unit testing and mocking tools. I've been a regular Rhino Mocks user for a long time, but I've seen lots of code samples with Moq and liked the syntax, so I gave it a try.
I have to say, I did prefer Moq slightly to Rhino Mocks. The newer Arrange, Act, Assert (AAA) style syntax in Rhino Mocks is a huge improvement over the old Record/Replay mess. But Moq has the benefit of being born at the right time and has AAA style calls without the burden of supporting deprecated syntax. This means Moq has cleaner documentation, fewer options, and fewer ways to get confused by the API. I really couldn't find anything I needed to do in Moq that I couldn't do. I did get a little tripped up having to get the object out of the mock, with myMock.Object calls, but that wasn't a big deal.
Here's the NuGet Moq install package syntax to add Moq to your unit test project:
I'm using mocking frameworks less these days. Instead, I'll write a fake object myself or just try to avoid interaction testing altogether. But if I needed to pull one off the shelf today, I'd grab Moq first.