I have tried all of the above but always go back to using pins - just works better for me. I lightly pin it working on the floor, then transfer it to my large dining room table. Then I pin the center quite well and quilt that. Next I bring it back to the table and repin the rest which takes care of any problems with it being nice and flat.
Before I start pinning I find the center of all 4 sides and then match the backing, batting and top at the marks. It works well for me. Of course, getting the quilt ready for quilting is the part I like the least but once it is under my needle on the DMQ, I love the actual quilting process.
Do what works for you and enjoy the process.