We have the HIX HT-400D. We love it! We wish we could have gotten a 16x20, but our apartment circuits wouldn't have taken it.
I'd say that most people here use an 8.5x11 printer and do just fine. I like larger prints, tho, so I personally prefer 11x17 transfers.
I do suggest getting a floating platten, otherwise on thicker garments like sweatshirts you may have issues with your transfer not pressing properly (not enough pressure in the front of your press).
Also, I highly suggest you get a teflon pillow the same size as your platten, and press with your garment on that. That will allow you to have your shirts' necklines on your lower plattens, and if you ever need to press hoodies with pockets or any garment with a sipper or bottons, you'll have no problems. The teflon pillow evens out the pressure across your entire garment.
