Once you get beyond keyboard shortcuts and stuff (which isn't the distro, it's the window/desktop manager), the thing to evaluate is the package manager (how are files laid out, how are releases done, how do rollbacks happen, how is the kernel updated, etc). Along with that, what init system is used, how sane the defaults are, etc. Beyond that, I think about how community packages work, and how good the documentation is for, well everything.

Ubuntu loses in every one of these categories for me compared to Arch.