I tried quilting with a round hoop and quilting without a hoop. What works best for me is a lap hoop. The one I have swivels on a wooden ball and is very easily adjusted for tilt and angle. This hoop leaves both hands free to quilt, plus there is virtually no obstruction to the underneath hand. My hoop is no longer made, but the closest thing to it is probably the Grace lap hoop. You can check out reviews of it on Amazon:
http://www.amazon.com/Grace-PolyPro-...dp/B002XNSJGE/ . Mine is all wood; I'm not sure if the plastic version grips the quilt as well as wood. Grace also makes an all-wood version of this frame.
I tried quilting without a hoop, but found that my stitches were considerably less even -- especially underneath.
In any hoop, a common beginner's mistake is to hoop too tightly -- like a drum. You want to have about 4" inches of "give" in the center of the hoop. A good rule is to allow the middle to move a fist's width down or up. This "give" in the quilt allows you to manipulate not only the needle with each stitch, but also the quilt (so you are also moving the quilt onto the needle).