I purchased from jiffyshirts and was very pleased with the product and super fast shipping. I think I had the shirts in 2 days. I then decided to do 1 more shirt for each member of our party and went all over town to multiple Wal-Marts, Target, anywhere that sold plain t-shirts trying to find shirts for each person's size and the color we wanted. The online purchase was sooo much easier.
I liked shirtsupplier.com better than jiffyshirts. (I found some pin holes in the jiffyshirts supply and their return policy wasn't as generous as shirtsupplier's return policy but that's just my experience.)
I also bought all of my shirts from Wal-Mart and Target. I have been very pleased with the way the transfers went on. I haven't washed them with the transfers on yet, but they washed well the first time.