First... Arch is ok (probably for many people). But it is not good. In my opinion, Debian is still the best option as universal solution.
Why NOT Arch? I quit because of the early adoption of systemd (yeah, sorry, please read on... this is not the only reason... it was the last thing that annoyed me much). My system could not boot up and shut down anymore (could not power off, ATX switch behind my PC was the only option; 5 secs power switch holding was not switching off, but rebooting... don't ask me how this is possible!! I always thought that this is hardware power-off, but I confirmed that booting init on Arch made everything work again). Arch followed the systemd path and did not let anyone decide, because of complexity reduction. I was forced to quit, because there was a dangerous tendency that my system would not work anymore (there are still race conditions that affect me in random patterns on systemd; I try it sometimes!).
The more important reason are the packagers. This is a unholy mess with them! I posted a bug report for a piece of software which was auto-assigned. The person did not want to care about it and unassigned. A core developer assigned him again and once again was unassigned. I mean I posted a FULL PATCH! Very trivial and it was confirmed that it solved many problems with the package by 2 people. I wondered wtf they were doing there. I never have seen such weird behavior. The small fix that takes about 5 mins to integrate was for several months unsolved.
I also looked at AUR, because Arch itself is lacking many packages that are interesting for me. AUR is a security catastrophe, of course, you need to take a look what you compile and install there (basically everyone can distribute anything without supervision). But it's not that bad, because you have at least an idea how to install something you need. The most annoying thing is that it is a mess. Old stuff that does not work, packages installing binary distribution from servers without any guarantees. AUR is a very dangerous facility and highly unstable.