Personally, I think the Maltron has a great shape. It’s not exactly perfect for my hands, but it’s very very good compared to anything else out there. [But note I’ve only used one for 5-10 minutes; no long-term expertise speaking here]
The Ergodox does have two big advantages though: (1) its two sides can be positioned arbitrarily relative to each-other, (2) it’s very easy to load any arbitrary firmware you want onto it, and change the layout to whatever you like, or add any special features you can think of.
Also, the Maltron is pretty light and hollow, which makes it slightly flimsy feeling (I’m sure someone could get used to this), and it doesn’t have my favorite switches on it.
I think overall the Maltron comes out ahead, especially if you put your own controller logic somewhere between it and the keyboard to allow for some programmability, but if I could make a dream keyboard, it would be constructed of some solid but not too heavy material, maybe wood, have switches something like the Model F but with the actuation point a bit higher in the stroke, be shaped somewhat like the Maltron (but with a few keys removed and some others rearranged to fit my hands perfectly), with the two sides tented, the center a bit higher than the edges, and would have some integrated pointing devices, I think one nice trackball in the middle plus a trackpoint near each index finger would work.
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I think the Maltron has a better shape than the Kinesis Advantage, and I figured out that the difference is mainly that the Maltron can arbitrarily position and orient its switches, because they’re stuck in a piece of molded plastic and hand wired, while the Advantage is hampered by needing to attach them to just a few curved PCBs. The Advantage tries to mitigate this with some keycaps of various profiles, but it doesn’t really make up the difference.
Also, at least for my hands, the Kinesis thumb keys are just in the wrong place and orientation, while the Maltron’s thumb keys are pretty good. Not perfect, but much better.
The Ergodox of course is worse then either one in shape for each hand (but with the advantage of independently movable halves). I think the Ergodox could be greatly improved even while sticking to two completely flat halves; it much too slavishly copies the general layout concept of the Kinesis, without adequately considering how to make keys easy to press on a flat design.