From a purely aesthetical point of view I'd choose Radz-at-Han. Unfortunately it also brings some bad memories with it (taking forever until you get the central teleport, which makes navigating the place 50% faster; and the overly stupid way they killed the Satrap while everybody else was suddenly moving in super slow motion).

The development of Mor Dhona sounds nice, but I haven't been around back then, so no fond memories for me.

In the end I'd choose Idyllshire. The place is beautiful in its own way, you can ride, and it has a nice feeling about it of different folks and people working together for a common goal.