I have an older Nolting with a 26" throat, that I bought from a friend. The first thing I did was add a stitch regulator. That was important to me.
If I could buy any one I wanted, I probably would look at the Millennium with the hydraulic table. I've tried all the machines at the International quilt festival in Houston for several years. The Millennium was the smoothest.
http://www.apqs.com/machines/millennium/
I have friends who have Gammills and Innovas. They would tell you to buy the ones they have. It all comes down to price and the feel to you. They will all have their off moments when the tension isn't right or maybe they just don't like the thread you are using and they just won't act right. The Innova with the computerized quilting program is one of the best buys.
http://www.innovalongarm.com/