Lol... who'd want Gustaberg... it's faster to get a Tele:Altep and Escape in Koroloka then to walk from that outpost...
I mean, you can't even use it until level 20, so it's only purpose seems to be garrison...
Ronfaur outpost has 'close' proximity to both Sandy and La Theine (elementals + Ordelle caves), and you can easily use it when going from Holla to Sandy (if you are sand oreo)
Saruta outpost has 'close' proximity to both Windy, harvesting points and giddeus...
Gustaberg outpost dumps you in the middle of nowhere, it takes 15 minutes to get to Bastok, Gusgen, or whatever...