If you're after durability I'd suggest going with the 2" and consider the T rack. I have done that and actually have the model where I can haul 5 bikes with confidence. My sister bought a Yakima rack and mounted a 1.25" receiver for it. With just two bikes I think you could just go with the 1.25".

I installed a 2" so I could pull some other small trailers (Jet skis, utility trailers, etc) if I wanted to so that might something to consider if that appeals to you.........