I like Devbox and I'm familiar with its features so I'll just mention the extras the mise has.
The ubi backend means I can use nearly any binary published on GitHub without needing to worry about a flake or nixpkgs. Just get the binary directly from the author. Same for many of the other backends https://mise.jdx.dev/dev-tools/backends/.
Tasks are very powerful, they can use dependencies, flags, args, completions, and watches. Also can be defined either as strings in the config or point to shell scripts or even python/node/whatever scripts.
The fact that mise doesn't depend on nix is both a blessing and a curse. I have less tools available and I don't have the power of a package manager, but on the flip side I don't need to deal with the idiosyncrasies of nix.
Thank you, TIL about ubi! My brain is now compiling a list of places where this will replace either a shell script or flake for my projects :).
Tasks sounds similar process-compose which is bundled into Devbox. I'll have to read up more on tasks though to see if that's an accurate assessment.
Nix is definitely a double-edged sword... One thing I like about Devbox is that it keeps Nix mostly (!) out of sight, mostly unless I want a binary from a GitHub release :).
FYI, ubi is just one of the backends. Besides many languages specific backends (cargo, go, ...), it has 3 backends that support generic packages - asdf, vfox and its own (core). Besides, the default backends are defined for many packages, so that you can let mise choose it for you.
I'm curious what some of the mise features are you like.