I max out Q first. However, I used to max out W before Riven's latest tweak, as it did a lot of damage at the expense of a very low cooldown. Now her W is weaker (though the stun remains the same), but the Q does more damage. In any case, even though I changed my mind when the patch came out, I still don't see any problem on maxing out W first.
...One thing though. If the enemy happens to be a pretty annoying poker, like Gangplank, I usually take 2 points early on E, just to block his Q, but need a pretty good timing for it and know when he's going to Q on you. I personally think it's worth it, as you'll be able to farm without big worries.