Hmmm! IMHO, the most desirable functionality is a single, toggle command which can be assigned a keyboard shortcut, working on the current line if none is selected or on all selected lines is. If any of these are already commented out, uncomment it!
Toggle, because obviously if it is already commented out, why would you want to comment it out again? Also in the opposite direction.
Yes I am sure Yutaka is listening. He always does, and that is not the least reason that I am using EE :-)