Hi. I only own and use the PM2 so I can only speak for that one

and Im not a fan of Quartermaster; not so much for all the knife dramas behind (which is nevertheless quite telling, interesting and entertaining to read

and lets consider its not only a Quartermaster thing, take Strider, for example

) but because I dont really like the style and technical solutions of most of their products (double/triple thumb studs, weird multiple grinds, Klingon/sci-fi blade shapes, excessive thicknesses, etc.).
But, as a knives hobbyist and no expert at all, when it comes to this comparison, I have to ask: are the two really comparable, besides overall size and weight? Looks to me materials are different (steel, handle, liners, etc.), locks are different, grinds are different, blade style/shape is different, etc. On papers it looks to me the Mr. Roper is slightly better (?) as far as handle materials (e.g. Ti vs. SS and G10) but, for my EDC use, worse in terms of cutting performances (blade steel, geometry, grind) and versatility (e.g. pocket clip positioning). I just can say my PM2 its a great knife, a laser beam and can withstand all the tasks I put her through performing flawlessly (my long version here:
http://www.bladeforums.com/forums/showthread.php/1383249-Spyderco-Paramilitary-2)
Never tried the Mr. Roper, so cant say

. It would be interesting for me to read/watch some users reviews (beyond the several table top show and tell)! If you go for that and will try it out I will read a report with pleasure! Good luck with your choice!