The "Best XP" or Best Gold" spot comes up a lot. I'd suggest just playing an area you like playing and you'll notice what seems to be working faster. Each class and build preforms a little differently plus there's playing style. There's a lot of grinding in the game so it's best not to worry about complicated equations over which map produces the most gold etc.
Places that have been suggested on this topic: Blue Rock Castle (Deserter hide out), Mercian Royal Crypt, Ursan areas (Nilomar Cape + Bloodpaw Cave), Maze of Lamth (Minotaur dungeon near Jabal), and the the upper north map areas that have wyverns that drop precious stones).