Eden would get my vote. Food is great and there is a buzzy atmosphere. The food is also good in the Mermaid, but the last couple of times I was there it was a bit atmosphere-less. I haven't heard of the Grangecon Cafe, but Wicklow is probably a bit far out of town unless you are driving.
Both Eden and the Mermaid Cafe are really good. For fresh food, locally prepared, good value, setting etc, have a look at the Winding Stair Restaurant. It is right by the ha'penny bridge. It is on a par with both of these restaurants