For touring single bikes, I have developed an affection for Continental Pasela's over the past two years due to their smooth ride feel. I run 700 x 35mm or 37mm on the front and 37mm on the rear. I carry a 35mm folding version as a spare for either end.

I mostly run the Marathon Plus's on the tandems and triples; typically in 26 x 1 3/4" on 48 spoke wheels. I don't remember ever flat'ing one of them, but agreed that they are a bit heavy and provide a good bit less in the way feel on the road (aka "dead"). A fair trade-off overall imho.