I'm a big Luclin fan, so I'd have to say DSP (Dawnshroud Peaks).
Alla here has a GREAT feature which you can check zones based on levels. Plus, if you're looking for an XP bonus and/or want to see if a zone has an XP bonus, you can check out:
http://www.rpgexpert.com/441.html
Dreadlands has some amazing XP, but I found it got slow at times, whereas I could level 30-50+ in DSP doing different camps and make some amazing plat off acrylia and pelts.
I'm also not one to 'push' my toons through the levels, as I tend to prefer to see and experience different zones. Another neat place is Sol A.
If you can put a group together, the cyclops' in Ocean of Tears offer some great xp and some ungodly loot (for your level). Plus with a good group, you can venture into Mistmoore Castle off of LFay. When I fought there, the xp and loot were great, but people constantly trained the zone, so you have always be ready for that.