However, Vicious Strikes means that you can sustained yourself. Many people make the mistake of engaging a low-health Olaf when he has vicious strikes up; he can just lifesteal his way through any sustained damage, and lifesteal faster the faster as he loses health. I've seen Olafs get to 1/3 health and not have their health move past that, all the while eating through an enemy. Reckless Swing spamming, on the other hand, actively drains your health as combat prolongs.
I think it's just that at LOWER levels, the output from E is more significant than the output from W.
But if you want to do the best of both worlds, alternate between W and E after you get the 3rd level of E?
Honestly, the E output is so nice early.