I was juggling this same question for quite awhile. Marans or Welsummer? Welsummer or Marans?
I finally decided on Welsummers, at least for now. I joined Marans-dedicated yahoo groups, Welsummer yahoo groups, and a general dark egglayer yahoo group. I searched the web, and listened to folks here. And here are the essential things I learned that helped my decision along --
1. Marans are undergoing a serious fad phase right now. Prices are through the ROOF.
2. Marans tend to be quite large birds -- I'm personally looking for more medium-sized birds.
3. Marans are said to be big time feed hogs -- not very efficient!
4. Only the well bred Marans have seriously dark eggs -- and, of course, those are the most expensive birds that you'll have to wait the longest for.
5. Welsummers are medium-sized, quite attractive, and have good personalities.
6. Welsummers lay reasonably dark eggs, and they are reasonably priced.
7. I love the "classic rooster" look of the Welsummer roos.
That's why *I* decided on Welsummers. I hope it helps with your decision!