The first, and biggest, question is: do you have the means to market yourself, or would you be relying on the POD site itself, and/or search engines, for whatever sales you might get? If the latter, then I'd say FAA is unfortunately, despite its serious problems and limitations, the only game in town.
FAA lets you set your own markup, and some people actually go there looking for wall art. I don't think both of those statements are true for any of the others.