From a Doo guy, gone t-Yamaha, gone Pol Pro, w/ some time on an early XP & non-broke-in XM:
For rider reference, I'm ~6'2", ~175# in gear.
I've owned ZX and Rev chassis Doos, and like most things, with enough time you get familiar with the chassis flaws [or feel] and how to work around them.
The Rev always had that nagging "I want to right myself and be on 2 skis" feeling and also had a bad 'balancing point'.
The Nytro chassis actually works quite well, the running boards were way too wide, but coming from a Summit Rev w/ wide boards, and A ZX w/ aftermarket tunnel and wide boards, I was familiar with the associated issues; hanging up in snow, awkward pivot points, and hanging up in snow.....
The Pro has been the biggest game changer for me. I really like the narrow 'everything'. I put my T-Nytro into some silly technical situations (by my own standards), but the Pro takes me even further, w/o boost. The Pro feels like its designed for "1-skiing". It really will side hill for miles on end, and that is what I love about the chassis.
XP, I didn't like it, at all. The flaws from the Rev felt more pronounced in the XP chassis. Harder time keeping it in a carve/on edge/1-ski. I really wanted nothing to do with the XP, another reason I left Doo.
Now, the bit of time I've had on an XM I feel like many of the pronounced issues I had with the XP are gone or at least largely negated. The easy of steering vs the Pro (or any other sled I've ridden) is really almost bizarre, like power steering; how'd they do that? Very easy to pick your way through trees at slow speeds (on 2 skis). Much easier to 'roll over' onto 1 ski, but still, I find it tends to want to correct itself (compared to the Nytro and Pro), but no where nearly as bad as the Rev or XP platform did. I find the steering a bit awkward after having so much time on the Pro, but that is a "get used to" sorta of problem more than anything. The XM engine/power delivery is so so smooth, its actually beautiful. Power didn't feel like it was ~20+ HP more to me, but it was applied so linearly that it feels quite different than the On/Off Polaris. I'd actually compare power transfer similar to a 4 stroke, which I feel have amazing midrange grunt [even a NA 4s]. The chassis still feels quite wide to me however, specially compared to the Pro, it just feels like there is a lot more between my legs, and my legs are bowed out in a weird way, even more so when there is some snow build up on the boards. Even the Nytro didn't feel as 'wide' to me. Maybe its largely the seat design? Aside from a few weird quirks or feelings however, I think with time I could get used to them and make it do anything I can do on a Pro. Engine and drivetrain reliability tend to be largely in favor of the XM [so far].
I still felt much more comfortable and confident on my Pro than the XM for technical stuff; going through 'ski wide' [tight] trees on the side of a hill, with 1 ski in the air, for example. But that comes with experience/time, and once you learn how and what any chassis will do when put into a similar situation, that would become less of a concern. With that said, my next sled will likely be an XM. Primarily because of reliability issues with the Pro...I really hate dealing w/ broken engines/down time, which was actually why I left Doo's for a 4 stroke in the first place. The XM really has come a long way since the XP in the chassis feel department if thats what you have for comparison. If your looking for a 13-14, I think either the Pro (with proper updates) or XM are going to do basically the same thing end of the day. I'd just feel a bit safer about the XM getting home under its own power. At least a broken "flex-skid" can be repaired and ridden out.. A broken driver, engine, or failed Belt drive however is going to be a day-ender. Not that I think a belt drive is a bad idea, it'll be great when the big 2 (or is it still 3?) have them on more of their sleds, but it just seems to have some teething issues.
