When comparing Yaourt vs yay, the Slant community recommends yay for most people. In the question“What are the best AUR helpers for Arch-based Linux distributions?” yay is ranked 1st while Yaourt is ranked 5th. The most important reason people chose yay is:
It's written in Go so it is fairly easy to add features or tweak this amazing tool.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Equivalent to pacman
Yaourt commands and flags match pacman, so it is immediately obvious how to use it.
Pro Colored output
Pro Adds seamless access to the AUR
Pro Can be set up upgrade your system with no additional prompts
Pro You can adapt PKGBUILD to your needs during the (pre-)installation process
Pro Supports backups
Pro Easy to add features
It's written in Go so it is fairly easy to add features or tweak this amazing tool.
Pro Intuitive CLI
Yay's commands and output make sense for anyone used to the pacman package manager.
Pro Written in Go
The compiled program is snappy while the source is easy to read.
Pro Available as a precompiled binary
Both yay and yay-bin are in the AUR, the latter of which doesn't require any dependencies or compilation, making installation and updates quick and painless.
Pro Yogurt interactive mode
Write package name without keys [yay <packagename>] to enter interactive mode.
Pro Doesn't rebuild already-installed apps like Trizen
Cons
Con Insecure
More information here.
Con Not maintained anymore
According to the Wiki page of Archlinux, Yaourt development is stalled.
Con Does not perform clean builds
Environment variables may get carried over while building a package, preventing successful building.
Con Bad split packages support
Con Written in Go
Running a Go program requires the Go runtime. Go is also a garbage collected language, so the program isn't as responsive as it could be.