I guess it come down to what other traits you value the most. I own both Welsumers and Marans. Welsumers are less expensive (typically) and it is a bit easier to find quality stock versus Marans. Also, with the birds I have had experience with, Welsumers seem to have far better temperment on average. My young kids can be around my welsumer roo (supervised, of course) can pick him up and he is perfectly fine with it. Maran roos temperment, however tend to very more greatly. I have had to relocate or more or less permanently confine to a run my roos because attempted to flog my kids or me. Obviously if are looking to make money, Marans would be the way to go. If not, I think the Welsumers (on average) tend to offer more (better temperment, less broody, higher laying rate ... in my experience, at least).
Z