Can't help with the models in question. I've been using a youth model 870 in 20 gauge for about ten years now. That youth model is pretty sweet when you get stuck in awkward positions in the turkey woods.
Bought my daughter an Affinity 20 gauge compact camo 26". If I remember it was $849 with tax. I get her the 26 cause I get her to shoot clays with it sometimes. Its a very nice gun she wacked two longbeards with it this spring with Federal HWT 7's on e at 26 yards one at 32. Good pattern to a little over 40 with one of Trulocks chokes. I've thought of leaving my Gold at home and taking it. Very nice gun would be a joy to carry around
Given the choice between the 2 I'd go with the franchi affinity. I've shot one in 20 ga, 26" bbl and it's a great handling, pointing, and shooting little autoloader. The guys on old gobbler seem to like them and pull pretty solid patterns with them out to 40 yds. You should be able to find one for $750ish in synthetic. Probably more if you want camo.
Dad had a Marlin Goose Gun. 10 guage bolt gun with a 36 inch barrel. It was pretty awesome for turkey shoots. Can't imagine a bolt gun being good for waterfowl like the name implies though.