I have an APQS Millennium and I love it. (I loved it so much I became a dealer! LOL!) APQS stand up machines are lightweight, move like melted butter, come standard with a phenomenal stitch regulator and is backed up by highly responsive, caring customer support. (yeah, I'm biased.
I really recommend you go to a show and lay your hands on each of the brands because picking out a machine is a personal thing. Pay sharp attention to how the vibration of the machine feels to your body. Also, read the warranty! Boring stuff but super important as there are MAJOR differences out there between warranties and if you are spending this much money... you want some backup.
One more thing, talk to owners of the machine, not just dealers. Find out why they bought that brand as they've been in your shoes and walked this path. Learn the good and the bad. Most machine brands have online forums. (Some will only let you in if you own the brand). Look at the resale value of the brand. Are they holding their value or are people having to slash the prices to sell their machines if they need to?
When test driving, try to make a diagonal line of stitching (that's one of the hardest things to do on any brand). How easy is it to control while making that diagonal line? Make circles with the machine and see how it feels to you. Just spend some quiet time moving the machine around and focusing on how it feels to YOU.
Oh, and don't forget to have fun with this process! Owning a good longarm machine is a wonderful adventure and my APQS Millennium makes my heart sing every time I turn her on!