Ashe Oppression or Juggernaut

They are almost never the same thing... Your 3% max HP and their 3% damage aren't equal(rare occurrences, obviously they will be).

There is a break even point, somewhere though.. I don't feel like doing the math.

You'd always have the 3% max health, but you may not always have the mana to maintain your Q. Juggernaut provides additional defense against all enemies, but Oppression only provides defense against movement-impaired ones.