There are various pros and cons for each level choice you make, and I will do my best to show nuances between each. To begin - we recommend selecting level 60-64, as your power level is strongest in this bracket. Level 64's with <25% xp to 65 receive the same mob hp as a level 60 with >25% xp to 61.
Most pure level in the bracket.
Requires being above 25% while locked to get the correct scaling.
No TWW enchants available* losing out on significant leech/speed bonuses compared to 61-64.
Great in Timewalking with lowest primary stat - competes with current season 3 max levels.
Relies primarily on 357 Green BOE socket/tertiary items as BIS gear, requiring hefty gold investments and AH scanning.
Able to readily use TWW enchants providing large power boosts such as 13% leech on any class.
More talents available than any other level at the same power level.
Can utilize TWW enchants on socket gear without relying on Green BOEs. (eg: 352 TBC socket gear can receive TWW enchants), saving on costs and providing more dungeon grind incentives.
Able to farm 344 green BOEs for usage by level 60s.
The War Within (TWW) gems and enchants are very expensive. This may be prohibitive to some users as gems run upwards of 2k gold each, and enchants between 2-5k gold. Choosing a 60 character with put less reliance on TWW enchants, but the gems will still be your BIS. This can save significant gold over time and is the recommend level choice to avoid TWW enchants/BOE purchasing as your farmed gear is near identical in power.
Written by @garzhod