I believe how you plan to carry the multi is the deciding factor.
In the pocket? Medium size is better for comfort
In a bag? Full size is better usefulness
I don't need a multitool in my pocket all the time just to be prepared for random stuff, so I like to keep it in my backpack that is usually a few feet from me. Therefore the medium size is pointless to me, so that eliminates the Spirit, Wave, Rebar, PST, etc. That leaves the Supertool, Surge, and Swisstool X. For me, I value the Victorinox qualities more than the Leatherman.
So I voted Swisstool X