I know nothing about Haven.

Warehouse 13 is okay. It's kitschy, but fun. It's more fantasy than science, which lets it get away with some of the things the artifacts can do. The plots are usually simple and predictable. As said before, it becomes better when Claudia joins the show. There are some nice one-liners. Overall, it's a show to watch if you just want some simple fun and not think too much. I like to watch it for that reason.