Yeah single target of course, Fire Mage DPS on cleave fights is so ludicrously high that it would skew the results. Fire is I believe still the premier single target Mage spec however until you get the trinket from Sinestra
, which reduces the base mana cost of your spells. According to top mage Arcane is perhaps viable for some fights with this trinket, fights with damage buffing burn phases such as Magmaw, where you can pop cooldowns and burst for a ridiculous amount.
Without the trinket Arcane is simply not mana efficient enough to compete with Fire over long fights, and seeing as how there are so many fights which have multiple targets or which require abit of AoE (Omnitron adds, Magmaw, Halfus, Valiona due to dotting the second drake with LB, Ascendant Council, Cho'gall and Nefarion are all examples of where Fire will almost certainly be superior) I am confident that Fire will still reign supreme until Blizzard gives the Arcane spec abit more of an overhaul.