I love the big and supportive community and the rolling release model.

Also lots of software between the official Repos and the AUR

Because it's actually simple to understand. There are different forms of complexity and one of the worst is when someone else has built something and you are trying to figure out how it works. Like Fedora, Ubuntu or whatever.

With arch you install the system yourself so you know what you have on it. Therefore problem solving is a lot easier. You put data into the config files so you know what you did.

People run their arch systems for years and never reinstalling. Sure, you will have some bugs but the arch wiki is amazing to help you fix them.

The community is incredible but also the fact that is a rolling release. You get to experience the latest and greatest of everything and don't need a big migration from a version to another.

The AUR package repository (user contributed) is huge and most of the time you can find an obscure little open source project in there but also commercial software nicely packaged for the distrib.

The stability of arch is impressive too. Often being a rolling release you fix problem along the way but as the steps are small they are well identified and quickly resolved. On Ubuntu when you do a distupgrade you are up for so much pain at once sometimes it might be hard to upgrade.

I hope it helps!