I've had little experience with the Pro Q E20s. I absolutely love them. It did take us a little playing with to perfect them, but it really wasn't that hard.
I have 4 Pro Q E 20's and one 18" WSM. I still have yet to use the WSM in the past 2 years. I'd much rather cook on the E 20 than any WSM, but that's probably just because I now know exactly how to use it.
I think both the WSM and the Pro Q E 20 have a fairly solid fan base. It really just comes down to your preference and learning how to control your fire/fuel. I'd strongly suggest learning to manually control your temps before going to a draft control system.
Oh yeah, you didnt mention this (or maybe I missed it). Fuel Source? Fuel type? Amount of fuel? How many stackers are you using for a cook? Water in the water pan?
The answers to these questions might allow us to help you out.