When comparing pikaur vs Pakku, the Slant community recommends pikaur for most people. In the question“What are the best AUR helpers for Arch-based Linux distributions?” pikaur is ranked 3rd while Pakku is ranked 10th.
Ranked in these QuestionsQuestion Ranking
Pros

Pro AUR package names in shell completion (bash, fish, zsh)

Pro Upgrade -git, -svn and other dev packages

Pro Using systemd dynamic users if building packages as root user

Pro Show unread Arch news before sysupgrade

Pro Interactively handle common build problems (like untrusted GPG key or checksum mismatch, wrong architecture)
Pro Can install packages even when others fail
Sometimes when building multiple unrelated packages, the failure of one means that none get installed. With this helper, it will not only ask you what to do during a failure, but you can skip the package all together without having to restart.
Pro Remove make dependencies on completion
Some AUR packages require at times dozens of dependencies solely for the build process. Usually, once the build process is done, they stick around without purpose. This helper automatically removes those dependencies once all the builds are complete.

Pro Retrieve PKGBUILDs from AUR and ABS (-G/--getpkgbuild)

Pro Build local PKGBUILDs with AUR deps (-P/--pkgbuild)
Pro Auto removes build dependencies
Has option to auto remove all unused build dependencies.
Pro Wraps pacman
Installation or updates of official or aur packages can all be done with pakku.
Pro Uses pacman interface
Easy to use for anyone familiar with pacman.
Cons

Con Splits pacman -Syu to -Sy and -Su
-Sy (to refresh package list first) and -Su (to install upgrades after user confirmed the package list or has been altered it via [M]anual package selection).
