If you're like me, you hate questing. It's not like you can't come back to them later if you need the gold etc. If you want to stop questing and take the quicker path, here's a few locations for you to level at. There is not really a minimum level, just be in a sensible range and at max 5 levels above.
Level 3 - 16- Stonefalls [Vivec's Antler]
Kill the Dreugh. You should be in a group of 3 maximum for the most EXP
Level 16 - 28Deeshan [Silent Mire]
Kill everything in this village. More mobs spawn around the water. In group of 2 if you can.
Level 24 - 34
Shadowfen [Sunscale Strand]
Run around this place and kill all of them. Can be in a group of 2 - 3. The less the better, just need to kill super fast.
Level 32 - 44
The Rift [Northwind Mine]
Run around this place like you did the above, and kill everything. Party size 2 - 3. If this place is too busy, you can also try Lost Prospect and kill the zombies in that area.
Level 40 - 50
Coldharbour [The Vile Laboratory]
Kill all the zombies in this area. Try and get there early in the morning if you can, as it can be quite busy! Any group size. Still good exp.
This is just my preferred route. You're welcome to get to any of the above places before you actually reach those levels. I'm pretty sure you'll still get EXP. This is great for questers also as you may be falling behind on zone levels. The levels stated above are just the maximum levels. I'd recommend you leave earlier personally, but yeah give it a try.