Ornate Defiant geared with J1 tank looking for a good spot to level and add AAs. I tried Grieg's End, but killing is very slow and mana intensive. I could start at the low-end part of the hole, but I spent way too many levels there long ago. Veksar always a possibility I guess, but I was thinking perhaps older planes?
Gunthak/Nadox, Velk's Lab, Acrylia Caverns... Plane of Innovation is perfect for that entire level range.
In general, go to the oldest zone you can find. Mobs have about 1/4 the hit points in classic zones as they do in some of the newer ones. I stay in classic or the lowest expansion I can for as long as I can whenever I level. At 50 you could do the drop side of the hole, which is awesome exp, and great loot. You can stay there till 65 easily. Velks lab is good at that level.....veksar zone in and then undead to 60, veksar once you get into it, is almost all single pulls, and a lot of undead.
The Hole and Veksar are your best bets. Veksar is higher level mobs but they also have more HP. Some better gear can be found there than Hole, but cash/gems is far better there than Veksar. If you're already rocking defiant, you're better off just grinding away at the ghost fort til level 60-65. Then grind away AA's til your heart's content.