I've got a NF NXS 5.5-22x50mm on mine... seems to work well enough.

One thing to consider is that the lower power scopes usually have more range of adjustment, which can come in handy if you want to shoot ultra long-range. The 5.5-22 has 95-100moa of adjustment, plus with an R1 reticle there is up to 30 moa more 'hold off' in the reticle. The 3.5-15x with the same reticle has 40 moa of hold off, and gawd-only knows how much internal range

I've been extremely tempted to stick my SS16x42 on there, though... that or one of the newer SIII fixed 20x w/ the modified mil-dot reticle.