Surprised Ergodox is not mentioned, that's the keyboard that started the movement. Very safe pick since firmware is open source and it can be both self-assembled and bought.

It has too many keys in thumb clusters and bottom row, but you can easily remove them.

I included ZSA's other boards (Moonlander and Voyager) since they seemed to have superseded the Ergodox in popularity. But yes, it definitely was one of the first to come out. ZSA is still a company paving ways though!

I feel like the Ergodox was traditionally a lot of people's first wacky split keyboard -- but for those that stuck around, it was rarely their last. These days, there are so many better options that it's hard to recommend Ergodox despite its historic importance.