It is really strange that you cannot have Stash generate a diff between two commits and have to go back to using git command line. It would be really helpful when working in a team environment to be able to send links to diffs around. This is a very basic feature I was shocked to find out that you can't currently do this in Stash. It seems like a very simple change since they already have diffs implemented, they just only let you select branches right now. They should be able to add the ability to select a commit instead.