Fun is subjective, but most popular? Got a source for that?
According to TF2's own statistics, payload maps like Upward and Barnblitz are more popular than Goldrush.
Either way, I don't see what a 24/7 Goldrush server could accomodate that Skial's Payload server can't, especially considering that since we used to have one, it likely died to a lack of players.
(I do find it odd that we have a 24/7 Dustbowl server still.)