I own a Swedish Marieholm 26 and have been aboard both the Contessa 26 and the Marieholm IF boat. The Marieholm 26 is beamier and has a higher freeboard than both the Contessa 26 and the IF boat. The the M26 is also marginally longer LOA. It displaces 5600 lbs, next to the IF boat's 4740 lbs and the Contessa 26 with 5,400 lbs.
I compared all these boats when making my buying decision. I live in Toronto and Contessa 26s are everywhere, so this was the natural choice, for a small offshore cruiser. Then I found a Marieholm 26 for sail in California and went down to have a look at it. I felt like most of the negatives (for me anyway) about the Contessa (no sliding hatch, no headroom, poor gallery, no bridge deck for a wet boat, tiny side decks for going forward) were all addressed and wonderfully executed in the Marieholm 26. There is no doubt that all of these boats are equally capable, but I found the accommodations design and overall build quality of the Marieholm 26 to be superior for my singlehanded live aboard purposes. Another nice thing about the Marieholms is that there hull deck joints are glassed together to form a solid joint which adds strength and prevents water ingress through toe rail bolts.
The major deference between the Marieholms and the Contessa are the rig. The Marieholms share a 7/8ths fractional rig and the Contessa is a masthead. The contessa's advantage is a larger foresail.
Obviously I'm a fan of the Marieholms. Just food for thought if you're in a buying position and afforded the chance to be considering all