I have the Pfaff that uses the Grand hoop, and can go 12x12. But I bought a 130x130 hoop (5x5) and wind up using that mostly. I digitized a lot of old quilting patterns and did those with the 5x5 hoop. It's good enough for the center of a large block, and you can always add strips and use the fancy stitches. Made a raggy using 9" blocks.
Go look at Embroidery Library. They have a huge collection of stuff and tutorials. See what you would mostly like to do - they sell in 4x4, 5x7, 6x10 sizes. Then you can judge which size would be best for you.
They have a lot of in the hoop and tutorials. There's a site online just for quilting in the hoop.
http://www.queenofstitching.com/component/virtuemart/?category_id=&page=shop.browse&manufacturer_id=1&limit=5&limitstart=0
The dealer will want to sell the "best" so find out your needs first.