I have both a Chinook 12' x 9.6' and a Guide Gear 12' x 12' tarp. I had the opportunity to pitch both of them over the weekend on a car camping trip I took with my family.
My personal opinion was that the Chinook tarp was far easier to pitch and use than the Guide Gear. In fairness, I have not yet had the opportunity to add loops to the Guide Gear tarp to make it easier to pitch as a rectangle. Even so, I felt like the Chinook tarp was better made and much easier to get taught then the Guide Gear.
This is all just my opinion, but I thought it might help someone who is trying to decide which one to buy.