I can't speak for the Marathon or Marathon Plus, but I've got some puncture-resistant experience to share.
We did a 400 km (250 miles) trip, over a dozen days, on various surfaces (more on that later) using Continental tires for the two bikes and Schwalbe Big Apple tires for the children trailer (Burley).
And we're really glad we did replace the standard tire from both bikes and trailer as we didn't experience any flat, we didn't re-inflate any of the tires even once.
Our trip was mostly hard dirt (maybe 60-65%), plus some asphalt or concrete (30-35%) and some gravel/sandy/other grounds. Overall, we didn't feel the tires to be heavy or anything like that, but we were heavily loaded anyway (trailer for me, rear bags for my companion), so it doesn't mean much. I can say I felt reduced drag from the trailer when we switched from the stock tires to the Schwalbe, as well as slightly smoother ride over gravel and lightly bumpy roads.
Now for the puncture part... With my 'big' trailer, I had to make my bike go over lots of thorny stuff to avoid holes and rocks and other hazards on the track, the worst part during about 15-20 kms (9-13 miles). So both my bike's wheels plus the left wheel of the trailer went over lots of thorns, and probably the other bike some also (as she hadn't a two-wheeled trailer behind, she was more free to avoid thorns, holes, rocks, etc. than me). And I hit a lot of 'bad' stones, some of them quite sharp, but always at reduced speed (< 10 kph / 6.25 mph) to avoid sending the trailer flying.
We didn't fully appreciate the puncture resistance before we met some other cyclists who just went over the same thorny/rocky/bumpy section as we did, and spent a lot of time fixing tires/tubes as all of them experienced punctures.
So we're very happy with our tires. I'm not 100% sure of the actual model of the Continental, GatorSkin doesn't ring a bell and the tread doesn't look right. I think they're in fact this: Continental Travel Contact. There is also a 'City' model: Continental City Ride. Note: I picked the website in search results, not suggesting it at all, we bought our bikes and had them fitted with new tires in a local bike shop.
Hope this helps :)