I never used Rails other than doing it's tutorial, etc. And I only know hotwire by their docs, so I can't do a real life / production code comparison.
But from my understanding, Unpoly manages to achieve almost the same thing that Turbo + turbo frames can do, plus some other extra goodies such as modals (now layers), forms validation, etc. I honestly like Unpoly a lot more, and it also works with any backend framework "as is", given it does not require any special behaviour from the backend. That's a big win in my opinion...learning a tool that can be used everywhere can't be a bad thing.
The only thing I miss in Unpoly, is something equivalent to Stimulus. You do have "compilers" which allow you to attach custom JavaScript to any Dom element, but everything you do there is pretty manual and imperative. For these use cases I also use Alpine.
But from my understanding, Unpoly manages to achieve almost the same thing that Turbo + turbo frames can do, plus some other extra goodies such as modals (now layers), forms validation, etc. I honestly like Unpoly a lot more, and it also works with any backend framework "as is", given it does not require any special behaviour from the backend. That's a big win in my opinion...learning a tool that can be used everywhere can't be a bad thing.
The only thing I miss in Unpoly, is something equivalent to Stimulus. You do have "compilers" which allow you to attach custom JavaScript to any Dom element, but everything you do there is pretty manual and imperative. For these use cases I also use Alpine.