The Gamma is the newest and parts will be easy to get.
I'd look into the Ektelon is worth looking into also. Its parts would also be easy to find as it is the older version of the Prince NEOS 1000 and aside from the smaller table, it is the same. Clamps are the same, tension head could be interchanged, etc.
If it were me, these are the questions I'd ask when trying to distinguish between the two. We've eliminated the other two; Eagnas & Zebest.
1) Are you going to string for others?
If not, either would work great unless your racquet has a fan pattern. If your racquet has a fan pattern, go with the Gamma. The glide bar vs. other clamping system. If not, go with the Ektelon. It will do a great job and be fast. BTW, there should be a badge under the turn table that says it is a MODEL D or DE.
2) What's the cost difference?
If it is significant, go with the cheaper. Both are good machines. The Ektelon is worth $300 easily. Does it have both long glide bars and two clamps? Not necessary but does it have the two shorter (1/2 size) glide bars? The Gamma is roughly $350 new.
3) Is speed a consideration while stringing? The Ektelon will be faster to string on and to learn to string on.
Another poster mentioned purchasing a Wise Tension Head. They were made to go on the Ektelon/Prince machines w/o any adapters. They go used for approx. $300 shipped. From what I'm reading here, I'm guessing that you have your option of any of these machines for approx. $200. For a total of $500, you could have an awesome stringer and as good as anyone has.
If it were me, I'd go with the Ektelon as long as I don't have to string fan pattern racquets and I might get it even if I did. There are many threads about the Model D or DE on here. The only shortcomings of these machines are if they don't have the Model H table upgrade. The picture you included does! I'd also look to see if it has the tension knob upgrade to show the individual tensions counting by 1s and not by 5s. Even so, that wouldn't be the deal breaker for me. The last shortcoming is the shorter tension arm to crank the machine back on but again, there are many threads and even Youtube videos showing how to overcome that slight deficiency.
Back to using POGs. Why did I ever leave you dear friend?