The Lodestar is the one that I think sounds the most interesting; I actually read the Savant, but didn't like it. Just didn't wow me like I'd hoped it would. The Mahout was interesting as well, but not my cup of tea in general.
Mahout, no question. A dedicated "pet master" class is one thing D&D lacks right now. There are pet master subclasses (beastmaster ranger, necromancer wizard, etc.), but each has a full-powered base class chassis, which means the pet is pretty limited in how strong it can be.
The others all look to me like they should be subclasses; specialized variants on concepts that already exist.
Gemini could be fun. We’ve got a similar concept in my current campaign: a two-headed ogre. At the start of each session he rolls randomly (50/50) to determine which head is in control of the character. One of them is a brutish warrior, the other a mage. During the session the player can reroll once, and the GM can reroll once. It’s been a lot of fun at the table.
The Savant. D&D 5e lacks a pure mundane intelligent based Class. I would design it by drawing inspiration from the Expert described in the Sidekicks UA, but without excessive skills in combat (I would leave those for some Subclasses, like the Tactician).
I tool like that Savant is an Intelligence based class, but the Mahout and Fate Bender are more my style.
Not sure why but many of the 'names' of these classes to not speak to me at all. Just hearing the name does not tell me what they do. Without reading about them I would have no idea what sort of character half of these would be.