Rhalgr's Reach

For me, it had the best aesthetic, the best music, was spacious so even with lots of players there, it never felt crowded or crampt, it has an FC chest (no other end game zone has one), and it was very easy when teleporting in to get your bearings to get where you wanted to go (unlike Eulemore which was the worst for this, always got so turned around when teleporting in)

Second would be Radz at Han, but it still gets a bit crampt since everyone just kind of hangs in the vendor alleys, plus the lightning in there does weird things to my color balance as I move around there.