I'll also tell you to avoid Nexus. It's just way too long and boring, even for someone like me who loved 1-5.
I'd go with 4, it's a little more interesting than 5 and has a fun world map to explore.
I enjoyed it quite a bit. The combat isn't amazing, but everything else is great (music/characters/setting/farming). Has that relaxing Atelier vibe to it.