There is no single "best way"; use whatever you like. Or perhaps a combination of methods, so as not to get bored. Which method is better also depends on whether your priority is to get magic experience fast, or to save money (or even earn money). Some of the methods are: fighting with magic spells; doing high alchemy; doing some of the enchantment spells; the Fist of Guthix activity (free, but somewhat slow); the members-only Mage Training Arena (this can actually earn you good money, reasonably fast).
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I believe the only requirement is 55 defence. You have gotta finish "The Fremennik Isles" quest too.
Either Tormented Demons or Mithril Dragons for their drops mainly. Also there are the godwars bosses too, even more then Armadyl Boss.
hween event (its too late to get it now)
It doesn't really matter, but I recommend around 49-62. Level 100 would be best too.
No, The server that runescape is based on is way, way too advanced to be hacked into giving out free items.