Clock Tower. New World caps out hard at 165ish because of the XP scaling based on monster level.
The bounty board is also hugely different, with 150 counts of big bells giving more than 150 counts of 4 monsters from bifrost tower 2.
It's safer/easier there, so you may want to stay until you're at the XP scaling cap. There is also a 40k hp difference between the mobs, so if you find you have to cast a skill too many times to kill big bells, that may be another reason to stick around.
There are monsters in the Verus maps that give a lot of XP too (in fact, some of the highest level non-boss mobs are there) but there is no bounty board and so the overall xp/hour may be low.
IMO, the last 10 levels are definitely from clock tower, but you may be able to squeeze 5 more from bifrost tower.
Edited by mildcontempt, 23 December 2016 - 06:21 PM.