The [community] repository has been removed. You can fix this by updating your /etc/pacman.conf file. Details are here:
Generally speaking, you should favour the official packages first (archlinux.org), if reliability is important to you. If you have more specific needs such as a custom build, -git version, or something not available in the official repos, then you might consider the AUR.
Discretion is needed when using the AUR though. Packages there can be added by anyone, so there is potential for abuse, although I’m not aware of any personally. The community is fairly self-regulating around that.