The grid I visit most often is OSGrid. I appreciate the stable grid servers that OSGrid provides. As the huge "central hub" of the OpenSim metaverse, OSGrid also has a large active community of Sci Fi enthusiasts and it attracts awesome content creators.
I have visited other OpenSim grids, mostly via HyperGrid, and some via grid accounts. I don't see any advantage to the Walled Garden grids and those grids that don't have HyperGrid. It is important to be able to save and backup my inventory as IAR files and my regions as OAR files. The grids that don't allow backing up my data or portable inventory are really not worth visiting, much less having a home or store on them.