As mentioned by others your best bet is to go to a show and try them both out unless you have access to both brands new by. I have the APQS right in my little town but went with the Innova after weighting the prices, quality, ease of movement, etc. I also went with MQR instead of Innova's AP due to the price plus I already had MQR on my 18" and could upgrade for a little more money. But trying out the machines to see what fit my way of quilting was the key. Then came to the point whether I wanted to fork out additional money for the upgraded stitch regulator LS or stick with what came with the setup. I called on some quilters in my areas to see if I could test out their system to see what worked best for me. Plus you can get some insight on the various add-ons this way as in the shows they normally have all the bells and whistles.
Plus with the Innova as mentioned you have 24/7 365 days a year with Customer Support and you only need to oil the bobbin area most times. There are numerous videos showing you how to time your machine and most everything else you might need to do. Not sure with the Gammill with how easy it is to maintain it. My fabric store nearby has the Gammill with Statler and they're very happy with it. So your best bet is to make a list of all you want on your machine, compare the 2 on quality, price, customer support and see who comes out the winner...........plus what feels good to you under your hands.