Feels like no blessing but the heart really has any big effect
I say stay with the XP blessing until you hit close to 100 and then switch. faster you can get to 100 the better. I think ill do that and then when I hit 100, swap to rare materials increase. to me everything else is meh....
I mean even 3% is better than 0%. With the current buffs to nightmare dungeons leveling is very easy even without no-lifing it. Additional 12% would be great. +5% from potions and +10% if you're leveling with friends. That's 27% increased xp. Raise it to 42% if you're doing legion events. Imho a bit too casual but still better than D3