I choose Fernando-he seems to have a great sense of humor and enjoys life. His overall personality seems to be well suited for matrimony-when he is ready to settle down anyway. It would be nice if Gisela is the one for him.
Ivan and Nickolay are the only two already married so they get points for commiting-Roger seems very comitted to Mirka too (but does he talk or is he the silent type? A guy who will talk about how he feels occasionaly is a real plus
Rafa is just too young yet but with time I'm sure he can make a good husband too. After James' last girlfriend, I think he may be in the stage where looks still trump personality. He may need to mature a bit too.
And rumors of his mother's influence may make it difficult for any girlfriend.
Of course in the end its just a guessing game based on their percieved personalities but its fun guess.