My own thoughts on the AI feature: https://connect.mozilla.org/t5/discussions/share-your-feedba... - LLM integrations can be useful and actually supporting end-users, but it must be based on entirely different paradigm (all about user agent automation, not a website in a sidebar) and it's probably best left out of the core application itself and rather be a external co-program.
As for the alternatives - to be honest, I don't really see much difference beyond various cosmetics. Both Zen and Floorp are basically the same Firefox for me, containing all the things I hate about Firefox ("sponsored" stuff everywhere, Firefox Account and Sync overengineering abomination, all the "safety" features that "protect" browser from its users, hardcoded built-in things that should be pluggable rather than fixed), while bringing nothing I actually care about and want to see (such as decluttering websites aggressively minimizing all the noise I don't care about - kinda like improved reader mode for everything by default, flexible automatic workflows for personal routine things, advanced history with optional content indexing for finding back things I vaguely remember seeing somewhere, automatic tab management to solve 100 open tabs problem, removal of tightly integrated bits like password or download management in favor of replaceable classic UNIX-way style external programs so I can use any tool I want while feeling those tools are properly truly and fully integrated and aren't some hacks like those password manager extensions messing with HTML).
Honestly, I'm sad that niche stuff like surf and Uzbl had essentially died, instead of evolving towards a pre-packaged "batteries included out of the box, but you can replace everything with your own" suites. I wished for a non-monolithic browser for technical/power users, with replaceable components for about a decade now - don't think I'll ever see it happening.