Roxitlc

C:  If I were buying a new machine it would be an Innova.  That being said, I'd be pretty happy with an APQS, A-1, Gammill, Nolting, or Prodigy.  There are things I like about each, and things I don't like.  I have an APQS Ult 2 ca. 1997, and a 2000 Gammill Classic.  Both were unregulated machines when I got them.  Helen and her husband Tony came to my house and studio in early 2011 and installed Intellistitch regulators on both.  The Intellistich regulator is great, and I'm happy with both.  The only thing I've had to do with them is replace a couple handle switches.
 
You might ask why I say Innova, and there are a few things unique about them that I like.  First the head turns on the Innova, so it can be removed from the table without removing the take-up roller.  I think maybe the Prodigy's head might also turn.  I also like the Lightning digital stitch regulator.  I like the table configuration as well, but I'm not quite so sure about the wheels.  I don't much like the "erector set" look of the table frame but that just cosmetic.  Now I must confess I've only removed the head of my Ult 2 from the table a couple of times, and never on my Gammill, so maybe the turning head feature really isn't a real winner.  I don't know about their service, but I've been told the machines are quite problem free.
 
APQS.  I don't like their horizontal wheel system.  It seems unnecessarily  complicated.  They've improved it somewhat by using linear bearings on the rails in their Bliss system.  But it is expensive.  I like their 4 roller system table.  I don't really like the batting access system (or more precisely lack of).  Their roller configuration accommodates it to some degree.  Also on models other than the Millie, there seems to be little adjustment capabilities on the rollers and rails.  What I DO like is their customer support and service.  It's absolutely great.
 
Gammill:  While their tables are well engineered and robust, the batting access system is a joke.  I don' think it was designed with how we quilt today in mind.  It could be improved, and made simpler by going to a 4 roller system like APQS.  The Gammill is strong and dependable.  I've heard people refer to them as the Mercedes of quilt machines. But I'd classify them more as the Peterbuilts of quilt machines.  
 
The A-1 is a nice machine, maybe the perfect size.  The table is very well built, but like the Gammill it's a 3 roller system which requires more adjustment, and adjustment mechanisms that wouldn't be necessary with a 4 roller system like the APQS, Innova or Prodigy.  Maybe it's the most user considerate table of all the makes.  I don't know much about their service though.  It's probably good, but pretty dependent on their MO headquarter.
 
The Nolting Pros are good machines.  They use Intellistitch regulators on this line, and the I/S is great.  Their tables are well made, but not nearly as refined as the A-1.  I think their service is probably quite good.  They've made pretty much the same machine/table system for quite some time, so they've had a long time to work out any issues, and I think it's pretty sound.
 
The Prodigy is a nice looking machine.  They have a very nice user friendly table.  Nice manual lift system (it can be power if you'd like).  The one thing holding the Prodigy back as far as I'm concerned, is their rigidly sticking to the L bobbin system.
 
I personally wouldn't consider any other manufacturer.  All the machines I've referenced are industrial quality machines built to last decades.  While I don't know first hand about support, I think all is pretty good.  I can't say that for some of the other machines out there.
 
Size is an interesting issue.  It probably has more to do with how and what you quilt than anything else.  I personally wouldn't want a machine that wouldn't sew at least 14 inches front to back.  Seventeen would probably be better.  You have to look at individual machine set ups to see what a machine can actually do.  Some smaller measured machines will actually sew a bigger field than other "larger" machines.  It has to do with the roller configuration and the "harp" shape of the machine.
 
You can feel pretty secure buying a used model of any of these machines.  If there's something wrong with the machine when you get it, it can be repaired and put back into excellent service, but probably there will be nothing wrong to begin with.  These machines don't break.  Pick a price point, and buy with confidence. 
 
This is my personal opinion.  I'm not promoting one machine over any other.  What I've said reflects the experience I've had, how I personally quilt, and my own personal likes and dislikes.  I'd probably be happy with any of them.  Jim