I know the Huawei Ascend W1 has a sizeable power pack, but its slightly beaten by the Lumia 720. The 720 features a large (2000 mAh) battery with lower powered internals. (same size as the higher powered 920 and the larger 625, which isn't too shabby either) Although the 720's battery is sealed unlike some other models.
But the W1 is lower cost, generally has less support than the stellar Nokia, and is a bit lower end. But the battery is still a force to be reckoned with at a sizeable 1950 mAh coupled with a smaller 4" display (like the 520).
Don't know about the W2 though.
I'd spring for the 720 unless cost and battery life is paramount above all else