Most definitely LaTale. I have been on and off playing that MMORPG since Freshman year in High School (Read: Late 2008). Whenever I got into Latale, I would usually spend at least 5 hours a day playing it, and sometimes nearly the whole day on weekends.
The only reason I am on break now is because I am waiting for the eagerly anticipated Season 2, which will basically be a complete overhaul of the current game, to rebalance classes, modify them entirely in their levels and skills, improve the quest system to make it a viable and realistically useful way of leveling your characters and earning money, as well as removing broken mechanics like the super easy leveling abuse method in the Coliseum and being able to farm bosses for large sums of money.
Basically, LaTale will go from just being fun, but often irksome, time-consuming and frustrating at times, to a very solid and playable game. And not to mention, the leveling will go much faster and work much more effifiently due to the power balancing of the characters, which will make the game much more accessible to people who want to play, but can't devote half of their waking lives to playing the game.
From what I've heard, it will basically be like the Big Bang update for Maple Story. I'm a bit irritated that is has now been over a year since the update hit in the Korean version.[sub]About December 15 2011 IIRC.[/sub] (It's a Korean game) I know that translations take a while, but considering how bad, to incomprehensible the translations can be at times, mainly when it comes to the story, and the fact that from what I heard, they aren't even going to bother making the effort to fully translate the story coupled with the fact that the Japanese and Chinese versions have already had the update for a long time just makes me think that they aren't even trying to get the update out at a reasonable time.