I've owned ErgoDox in the "default Massdrop configuration", then Kinesis Advantage, then something like Humble Hacker, now ErgoDox again, but with 80 switches and sculpted keycaps this time.
There are three reasons why I don't have the kinesis anymore: size, not enough keys, and firmware.
First, size. Kinesis Advantage is bulky, the empty space in the middle isn't flat, and the keyboard is tall; I didn't like the angles either... resting my palms hurt... In the end, I had to lower my keyboard tray, put something like a towel under the front part of the keyboard to get somewhat negative tilt comfortable for floating hands, and put a thick book under my mousepad to avoid wrist extension while mousing.
Second, keys and firmware. This largely depends on your use case. I heavily use AltGr (and AltGr+Shift) to type letters with diacritic marks and proper typographic symbols (esp. quotation marks), thus symmetrically placed AltGr keys are very useful. I also prefer to have special symbols like parenthesis or brackets around the home row (on a layer, of course)... another pair of modifiers required. Moreover, hotkeys for window management, navigation and stuff like that are neat too... another pair of modifiers. My hands are slightly smaller than average, I can reach the outer thumb keys on neither the kinesis, nor ergodox. When I remapped outer 1.25x pinkie-controlled keys (e.g., Caps Lock) to modifiers, it exposed some bugs in the firmware (or maybe keyboard matrix? Idk), and even other key combinations stopped being registered at times.
80-key ErgoDox fixes both issues. I only wish there were extra keys between main and thumb clusters. That gets you something pretty close to keyboard.io.
The Advantage of Kinesis Advantage is that it isn't flat. Keywells are neat, but I can live without them easily. Thumb keys on a different plane are a bigger deal though, and they're the reason why I'm considering Axios or Maltron. Thumb clusters made with the gripping motion of an opposable thumb in mind are truly a killer feature in my eyes. It's one of the main differences between Logitech TrackMan Marble FX and Microsoft Trackball Explorer; the latter doesn't cause me thumb pain every now and then.