fastest leveling imo
1-5 lizardman trackers (outskirts or agans ring, to the south, and also to the southeast.. you can hit the grass snakes till level 3 if char is weak, then go to lizzy hunters than trackers... past level 2 trackers get you 120-134 xp points, and arent tough, so it goes fast... plus ive seen them drop stat runes more than once)
5-10 grobolds (main or secondary camps, just a ways northeast of hamlet of calder or caldaar? forget spelling... anyways, youll level fast here, as long as your char is superweak, once you hit 10 though it slows alot... watch out for LoD though, they often have a level 15-22 sitting at the main grob camp, screwing up leveling for anyone there... grobs will net you from 300-1000 xp a kill, depending on which camp you hit)
10-13 bog rats (wererat or ratcatcher camps, the ratcatcher camp has more spawns, so you can level faster... its a ways northeast of the wererat camp, they dont agro so its pretty easy... net you about 1500 per kill )
13-21 nailtooths (theres r1 and r2 nailtooths that should cover the entire teen spread... if you're lucky you may find a cyclops group)
i did lvls 1-13 almost entirely solo with my current elf char, so unless your char is setup poorly, anyone should be able to manage.