Well, actually none of the options... first you download it, for free, then you play it online (it cannot be played offline). Playing is for free, but you can purchase some packs that can make your game, let's say, a little easier.
GREAT addictive game, played it a couple of years. there is not really a "best" character. depens how you like to play. agile and fast = blader, big powerhouse = warrior, etc. easyest to start with are the archers and wiz. saves you time walking to monster because you attack from a distance. my favorite are the blader and force blader, because they are just a cabal version of Danté (of Devil may cry)