I think that it is important to consider another option as well. Let the Developers teach other their specific test framework(test automation tool), this way they can all see the strengths in the specific tool while learning something that they can bring into their testing framework/tool.
I do agree with @Bookeater's answer as well, but think it is important to Learn about new things because that technologies and languages that are being used are changing constantly, so to be stuck in a single language or framework isn't beneficial either, in my opinion.
I believe that the Testers themselves should help to make the decision as to what testing framework(s) that you use. letting them learn and look at each of the frameworks let's them figure out for themselves what the better framework is going to be to test the specific applications.
What I have been trying to get to is that they can help you decide which framework will work better for them and the applications, and also which one will be easier to standardize as well.