Dungeons are fairly poor for leveling, between having to queue up and the general length of them compared to reward.. they're kinda not worth it for anything other than completing quests and logs. Standard grinding though, is highly underrated! A good group of 8 people can cause massive havoc together, and if you find a good spot you can rake in the EXP very quickly. The only problem I see with normal grinding is that it ultimately has a higher repair cost, due to the fact damage is more evenly distributed between people. (FATE's keep repair costs generally low, unless you're tanking things. Which never happens unless it's a FATE boss.)