Signal strength varies along the coast, of course, and is best near inhabited areas.
And I've been told that here on FINNMARKEN it is best by the sofa wall in reception, and maybe in the cabins in that area? Also in the cafeteria on deck 4 and Babettes Kafe on deck 7. I'm sitting at the table right next to the cake display, and here signal strength is very good.
If you know something about WIFI on the other ships and can be bothered to do so, please write about it in the comment section.