ST has more sporting pretentions than the Multi.
Didn't like the seating position on the ST3 I tried out as it was quite a stretch to the bars and, after the 998, my back now prefers the slight lean forward/upright style of the Multi. It's much more at home commuting and on twisty roads, not bad on high speed motorways etc but you can change the screen to help that.
Get a Multi
check out
http://www.multistrada.net/