I rode across the country on a pair (two pairs actually, first set wore out) of marathon pluses. I got 1 flat from a metal staple, which is pretty good for 4200 miles :D
The non-Plus Marathons are quite nice, but less puncture-proof.
You can't really win, the stiffer the tire the better it is at protecting the tube but the rolling resistance is higher and the tire flexes less which makes it less grippy.
Weirdly, it's actual black magic - the regular Marathons have the lowest rolling resistance of any touring tyre[0](lower than Schwalbe's own Marathon Racer lol), despite being very good at puncture proofing and not being completely slick. No idea how Schwalbe has actually done it.
