I'm with Biggsy on this. I currently use Marathon Plus 25s, but I'm going back to 28s next time they wear out. The protection is second to none, but there is a slight rolling resistance problem, and the sidewalls are ridiculously thick. Yes, something like a Pasela, with protection comparable to an M+ (fit & forget), but less fragile sidewalls (albeit black, as Biggsy suggests) would be a great tyre. Sizes from 23 to 35 would probably cover the market.
I ask a lot of the rubber I ride. It has to cope with the potholes of London, for a start, and occasional touring, as well as the occasional bit of roughstuff. M+ is the only one on the market that actually fits the bill.