Of the 3 developers I mentioned Softube is my least favourite, but I do love the Summit Audio Grand Channel. Their idea of “analog modelling” is basically adding noise (H-Series plugins are a good example).
They thought they’d be able to ride their early success forever, and by the time they realized their competitors had completely eclipsed them it was too late. They’re kind of like North American car manufacturers. It can get super complicated if you try to do too much with it, but I prefer to keep it simple and (mostly) just stick to the distortion options unless I have a specific goal in mind with the rest of the features and already know how to get there. It's a suite centered primarily around multiband distortion (with a ton of character options) as well as a flexible signal routing for different filters, delays, IRs, and compression.
If I'm looking for some more gritty harmonocs with a lot of flexibility in the character of the distortion that's generated, I use izotope's Trash 2. For something quick and simple where I'm just adding high end harmonics with a single knob, I use Slate's Revival. It's a multiband harmonic generator that's super flexible, but takes some time to adjust to. For clean harmonics on the high/mids similar to the standard result of maxxbass, RBass, and LoAir on the contrary end of the frequency spectrum, I typically reach for Waves Vitamin.