I am from the Netherlands, and frankly, both Marieken and Mariken (especially the latter) are old-fashioned variants of the much more modern name
Marieke. That said, I think I like Mariken best, and think it would be easiest for non-Dutch people to pronounce. It's also the name of Mariken van Nieumeghen (modern Dutch:
Marieke van Nijmegen), the lead character of a well-known 16th century Dutch play. :)