Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
I believe with a good team (premade) AP is better. His spells scale better and your Q only suffers early game. Your auto attacks are pretty ****py, but I feel the attack speed from his passive and the fact I normally push towers with a lane mate or two allows me to increase our attack speeds and down the towers quickly enough. When my Ult is up and no one is particularly low health and people are sitting in their lanes I'll usually send it down the lane I am in which usually kills the creeps and gives me gold along with damaging the enemy champions, sometimes enough to make them recall back to base.
I use AD when I solo queue because relying on random people to do anything right is far too taxing.
The reason I take exhaust is because no one else on my team normally takes it and I don't find the extra point in crit to be too helpful.
For my item build I usually start off getting tear->sorc shoes->Archangle's staff but I am not sure if Haunting Guise will be worth it over Tear early game. It seems that it would be considering the early magic pen and spell-life steal. My last two items I switch around, depending if the team is stacking MR or not.
As of a couple games getting Haunting Guise first I realized that I was quickly going OOM and now tend to get it before Lich Bane.