Considering how his playstyle revolves around it, Aatrox W is weak in comparison to similar spells.
Every third attack, EITHER:
Heal yourself for 20/25/30/35/40 (+25% bonus AD), 60/75/90/105/120 (+75% bonus AD) when below 50% health.
or
Deal 15/23.75/32.5/41.25/50 (+25% bonus AD) true damage to yourself, and deal 60/95/130/165/200 (+100% bonus AD) bonus physical damage.
meanwhile, other champions with combined onhit damage and healing,
Every third attack, heal for 30/35/40/45/50 (+20% Bonus AD) (+40% AP) AND crit for 125/137.5/150/162.5/175% damage.
(Additionally, has an active attack speed steroid on the same spell that grants as much attack speed as Aatrox's ult.)
EVERY attack, heal for 5/7/9/11/13, or 10/14/18/22/26 while active (over the course of 3 attacks, heal for 78 health).
When active, additionally deal 15/30/45/60/75 true damage (over the course of 3 attacks, deal 225 true damage).
Aatrox has to chose between damage and healing; I can accept that. But if that is the case, why are his effects weaker than those who don't even have to choose?
His heal is complete ass if he isn't low on health, and while the AD ratio on his blood price is high, he can't really build much flat AD without killing himself.