Be careful now. You're begining to get into apples and oranges of tires.
There is no comparison between Conti 4-Seasons and Schwalbe Marathon Plus. They are designed with completely different buyers in mind.
Every tire is a compromise. The 4-Seasons prioritize in the direction of weight, giving up something on the puncture resistance and tread life sides. The Marathon Plus prioritizes in exactly the opposite direction.
As a result, a 28mm 4-Seasons weighs 260 grams, will likely last 2500 to 3500 miles in the rear (based on my experience) and will occassionaly get punctured. (Typically once per tire in its lifetime, in primarily urban commuting, based on my experience.)
The Marathon Plus in 28mm weighs 740 grams, and based on reports here, will likely last 7500 miles in the rear and will never flat.
Both tires get good ratings from their intended buyers, and both tires get poor ratings from those who prefer the other one.
Which is the "better" tire depends on how you prioritize weight, puncture resistance, tread life, and grip.
I guess its easy to get into a apples to oranges comparison, or at least a comparison of very different apples if I start comparing different brands and models of tires.
One thing is for sure, what I have learned from this thread has convinced me to get a wider tire, likely 28 or 32s depending on the tire I pick. It has also told me a bit more about setting my pressure. It has also gotten me to think about getting different tires for the rainy vs dry season (aka winter vs summer). Thanks to all who provided great info.
That brings me to my next challenge, choosing the tire. I was going to originally get whatever my LBS recommended, but now I realize I need to do a bit more thinking about my needs to select the right tire (or tires). I also need to decide if I want to buy local or order online, as that could change my options. Now to research tires, and to keep this thread on topic maybe start a new thread for advice on what tire (sure to get into a heated discussion!).