I have a 13 pro 155, came off an Switchback assault. Dad rides the switchback Pro R Switchback and mom the Rush.
The honest truth from what I have seen in my seat time breaks Down Like this
155- easily the best handling in the real snow, ok trail manners soft suspension for ditch banging and field riding, slowest top end, best stock power
144- a good compromise between trail handling and deep snow abilities, not the best at either, but a solid second place. With the right track still a ton of fun in the deep. Will handle ditches at 80mph all day long and stand up to
136-I seem to think its the best handing on trail, even over the 121 rush, could be just minor suspension setup tho, and yes setup is that important on these. Good and fast, takes a beating and asks for more. Lacks the deep snow abilities of the longer tracks. Feels heavy in the front end in powder
121-all the same as the 136 but less deep snow capability, also this is 600 and the rest are all 800
And just to clarify what exactly those sleds were
13 155 pro- 645 miles of seat time
12 switchback pro r (dads) ~200 miles seal time
11/12 switchback assaults ~ 2200 miles seat time
10 600 rush- (moms) ~150 miles seat time