I bought Ez the day he came out and spent some time trying to figure out what is best on him. After some trials I decided that AP is the way to go. Although I have seen plenty of strong DPS builds on him, this build has only a slightly lower auto attack damage, but the lichbane coupled with Mystic Shot+Cooldown Reduction allows you to hit for around 500 to 600 every 1.5 seconds.
(Rod of ages was a hard choice. Usually I would build lichbane first, which you can do if you want a higher damage output early, but Rod of Ages allows for the staying power needed late in the game and early game pretty much prevents you from dieing.)
So I decided to drop Rod of Ages because on someone like EZ damage is more important. With the lichebane first you deal tons of damage and then the rylis allows for the staying power that Ages once provided.
Ez not only has a built in escape mechanism, Arcane Shift, but if you throw in flash you have 2 fast teleports to keep you alive OR attack someone and prevent them from escaping. The other main reason to go AP is Trueshot. It has a 1 to 1 AP ratio and can easily do around 800 or 900 damage when maxed out. This is a powerful tool for attacking champions, initiating, or even clearing out minions attacking a tower from across the map.
When in team fights I tend to begin, if they are clustered up, with Trueshot. This gives your team around a 500 hp advantage in the beginning of the fight. Once in the fight, as usual, spam Mystic Shot as often as possible even if it means attacking a minion. This is because of the cooldown added by Mystic Shot. Every time you hit something with it cooldowns are reduced by 1, so after about 20 hits you get your ult back, counting Mystic Shots cooldown time. In addition to Mystic Shot use Essence Flux a lot. When picking targets you want to hit their dps, or your dps. A 40% reduced attack speed could bring a twitch from 2.5 to 1.5 making him much less lethal. Don't forget it works both ways. Arcane Shift should really only be used for chasing or escaping, so don't bother too much with it in team fights.
PS this is a build in progress but I still feel that AP EZ is always going to be better then simply DPS