Guild Wars Factions

The Factions campaign gives access to the Assassin and Ritualist professions. Unlike Prophecies, progress to level 20 takes a very short amount of time. Early quests give plenty of gold that you can buy skills with (very few skills are awarded for free). Elite skills also become available early, although the bulk of them come much later. Access to other campaigns occur very early, just a little after you leave the starting region of Shing Jea Island. A good campaign to start from to quickly get to level 20.

The problem with leveling up so fast is that it is not beginner-friendly. The starting region does not offer a lot of opportunities for new players to get used to their characters before being thrust into the mainland Cantha (which might surprise unprepared players due to the jump in difficulty). And without skill rewards, players are left to their own devices when deciding whether or not to buy new skills - possibly a good thing for experienced players, but much less so for inexperienced players. All non-elite skills can be purchased in Kaineng City.

http://wiki.guildwars.com/wiki/Guide_to_character_creation