ultimately there is no 'good' place anywhere in game, since by the time you're high enough to fight higher monsters, they are't giving good exp either, this game is set up for those with money to spend - real and game and you won't get decent points until you're got goddess powers and you need to be lev60+ full team to do that, else a 90+ team with revive to drag you through supposing you don't get over killed and teleport back to save point

ultimately you must be prepared to spend lots of time - though there is a guide by the ultimate gamer group or whatever they call themselves - lev1-70 in a week, but that was with spending real money