Depends on your play style. Paladins can be overpowered sometimes, but at low levels like 19, they don't have a lot of attacks. Hunters can be good if done right along with rogues and mages. Priests are better for healing like druids and to a lesser extent shaman. shaman can be a twinked, but since their totems are not mobile, they might server better as base/flag defense than just smashing other people out in the open.
Just remember, if you twink, you will want to turn off XP. The drawback is that you will only fight other twinks who have also selected to turn off XP. This can make the que times extremely long.
Rogue = quite good as a twink :D
Tanaris
Outlands..Hellfire Peninsula
stranglethorn vale or dustwallow marsh.
that is illegal srry but it is
If you really want to make some good money on World of Warcraft, the best way to get it is to just level. Once you level to about 50, you can sell heaps of items that you get off monsters to the auction house. You'll make loads.
Mine cobalt ore in Borean Tundra and Howling Fjord. The areas are loaded with it.
World of Warcraft lore can be found at the official World of Warcraft website, along with other sites, but it is a good place to start. On the official site they have the history and lore of the Warcraft Universe.
For guides on World of Warcraft, try the site in the related links below.
world of warcraft
Where you level depends on what race/faction you are and where you started. There was a very good overview map on MMO-Champion; I have placed it in the related links.
There is a good world of warcraft guide on http://www.hiddenstuff.com/ that will teach you how to do this. hope it helps!