Sins its only 20 minutes, go for Rogue and go for Troll rogue, u have both the best "start skills" as a rogue, and u get berserking racial that u will use 10 times (increse attackspeed by 10-30%). Durotar is full of mobbs, especially in the lvl 1-6 area wich u probably wont leave in those 20 minutes. Recomendation: If u really whant to winn that Tournament, try level a few times for 20 minutes and see how far u get.

GL

-Emo?