When comparing XBPS vs Flatpak, the Slant community recommends XBPS for most people. In the question“What are the best Linux package managers?” XBPS is ranked 7th while Flatpak is ranked 12th.
Ranked in these QuestionsQuestion Ranking
Pro Extremely fast
Pro Can Detect Incompatibilities
XBPS can detect incompatible shared libraries or dependencies and gives you options before installing.
Pro Can Install Binaries or Build From Source
When installing software you can choose to install binaries or build it from source (natively or cross-compiled).
Pro Written from scratch
Pro Lots of features
XBPS can not only be used for installing/removing packages, but it can query for package info (such as version, dependencies, size etc), reconfigure packages, report and fix issues by modifying the package database, search for alternatives, manage local repositories and various other useful tools.
You can install flatpak packages on any distro you want.
Pro Application sandboxing
All applications are limited to a set of predefined permissions, enhancing privacy and security.
Pro A well-written documentation
Pro Flexible runtime management
You can install a lot of runtimes for different apps, making applications a lot more compatible while still allowing some applications to share their runtimes.
Con Not just one command to run
It's not a very big drawback, just not as convenient as one command with multiple options to remove and search for apps.
Due to the way Flatpack handles packaging, this can lead to a large cache being created which quickly inflates to unreasonable sizes. Not only this, but using flatpack requires a large chunk of space to be reserved for it's own file hierarchy.