I have standard Marathons in 28mm on my audax bike (I've been advised several times to go with a lighter, racier tyre but I like the puncture resistance), also used them on folding bikes (20x1.75) for commuting. Good, solid tyres, never had a puncture and roll well.
On the hybrid and my Raleigh tourer I have Marathon Plus in 35mm and 32mm respectively. The Plus tyres are simply bombproof. I understand they have a very strong sidewall which means they are excellent for a heavily loaded bike. I must say though that standard Marathons work fine with heavy loads too, though if I was cycling for an extended period with luggage eg. cycle camping, fully loaded touring, the Plus tyres would provide peace of mind.
I do have a pair of Gatorskins too on my single speed, which will be transferred to my 'training' road bike soon. Seem pretty robust and lighter than a Marathon Plus. Slicker tyre than the Marathon.
Standard Marathon comes in 700 x 23c, though I've never used that size. Marathon and Marathon Plus both in 25c. So there's one to suit just about every bike. Understandably there are riders who find the tyres too heavy or don't like the way they handle. Personally I like them and don't really notice the weight. If I was riding a bike I could pick up with my little finger I might feel differently of course...