Distribution Purpose
Both of these Linux distributions follow a different philosophy: The Debian community abides by the Debian Social Contract, whose first line states that Debian and all of its components will forever remain 100 percent free. The Arch Linux community embraces the KISS principle (Keep It Simple, Stupid), striving for an elegant, minimal distribution that can be molded according to users’ preferences.
Since November 2017, Arch Linux supports only the AMD64 & Intel 64 (also called amd64) architecture. In contrast, Debian officially supports not only the AMD64 & Intel 64 architecture, but also Intel x86, ARM, ARM with hardware FPU, 64bit ARM, MIPS, IBM/Motorola PowerPC, Power Systems, and 64bit IBM S/390. Many other architectures are additionally supported by non-official Debian ports.
Software
Unlike Arch Linux, which is a rolling-release distribution that only contains bleeding-edge software, Debian comes in three distinct branches: Stable, Testing, and Unstable. The Stable branch contains only well-tested software that has been in the Testing branch for at least several months, ensuring that most bugs are already squashed. The Testing branch is continually updated until it is frozen for a few months before it becomes the Stable branch. The Unstable branch is where most packages start, and it is also where recent software releases can be found.
The rolling-release nature of Arch Linux makes it particularly suitable for desktop users who want to stay on the bleeding-edge of Linux software and like the fact that they don’t have to deal with a major update every year or two. Instead, software updates are available as soon as they hit the repositories, which is usually only a short while after they are released.
Package Management
The Debian packaging system relies on the apt-get program to provide users with tools for searching and managing packages—all 68,000 of them. Arch users rely on the pacman package manager, but the official repositories of Arch Linux only contain around 10,000 packages.
However, Arch Linux makes up for it with its ports system, called Arch User Repository (AUR). AUR is a community-driven repository with more than 43,000 packages that takes care of downloading, unpacking, patching, compiling, and packaging software.
Software from AUR can be installed either manually or using an AUR helper, which is special package manager that automates the AUR build process.
Installation
Arch Linux has gained notoriety for its barebones installation process, which takes place entirely in the command line and requires the ability to follow detailed instructions to a tee. The installation system of Arch Linux installs only a minimal base, and all other components, such as a desktop environment, must be installed manually by the user. Debian is much easier to install thanks to the Debian-Installer installation program, which guides the user through a series of relatively simple steps.
Documentation
But even though Debian is easier to install than Arch Linux, its documentation leaves a lot to be desired. According to Debian project leader Chris Lamb, “[Debian developers] should always be asking [themselves] the difficult questions such as why the Debian Wiki did not become the much-lauded Arch Linux Wiki.”
Indeed, the Arch Linux wiki has become an invaluable repository of Linux-related knowledge. The wiki covers everything from Arch Linux installation to post-installation tutorials to general administration to common problems to various Linux applications.
Conclusion
In contrast with its overwhelming presence on servers, Debian is not nearly as popular on the desktop as it once used to be. Most Linux users prefer bleeding-edge software over bullet-proof stability, and Arch Linux satisfies this demand perfectly. But when it comes to supported platforms, user base size, and the number of packages in official repositories, Debian has an edge.
