I have the 6 quart Pro models. That extra quart really makes a difference. I do wish they had flip top heads though.
Do I have to choose one? If I do.. my Ateco fondant Mat. Has made my life so much easier. My 6 qt kitchen aid is not far behind it though. I have so many tools and toys that I would have a hard time doing without any but these two are my favs.
the model that I have... is the kitchen aid professional 600... and I have a standard kitchen aid too that I use for smaller jobs. Love them both.