Definitely pixi imo. At least for me it works just as well as uv and imo does even more than uv by giving you the ability to mix dependencies from pypi.org and Conda. And the great thing about Conda is that they still build PyTorch for Intel Macs or OpenCV for macOS 11+ which is not the case for the wheels you'll find on pypi.org so it's really great if you want to build software that is shipped to a variety of old platforms.
pixi offloads PyPI ecosystem stuff to uv, but pixi is conda first. The team were actually the first to build a Rust based Python package resolver (rip), but after uv was released they migrated to uv's resolver (Python package resolvers are hard and a lot of work to build and must be tested against the whole ecosystem).
It literally says on the homepage/the page you linked, that pixi is just a frontend for uv in the background to interface with PyPI and the project TOML files.
that isn't quite true, it defaults to conda packages (and so supports non-pypi things, its main advantage), I believe only when you are mixing these with pypi packages does it then also use the same resolution library backend as uv (and indeed directly at the rust level) https://pixi.prefix.dev/latest/concepts/conda_pypi/
Have not tried it too much yet because I was pretty content with `uv`, but I've heard lots of good things about it