Aside from the different desktop environments, you’ll run into, the biggest difference is the package manager. Arch’s package manager will let you download whatever you want and push out the latest updates very quickly. Apt, on the other hand, is much more conservative and restrictive. If you want the latest version of a given piece of software, you’re going to have to ask the Arch devs to package it, which can take anywhere from a couple of days to several months. So, why choose one over the other? I’d say it’s a trade-off. When you’re in a Debian-based environment (like Ubuntu, the vast majority of Fedora/CentOS/RedHat-based systems, Debian itself, and so on), the updates will just come straight to you automatically. No waiting around to see if it’s compatible with what you’re running, or if you even have the right architecture or driver for it. Even if you’re not running Debian, though, package updates are still a pretty large reason to choose Arch.
It’s also less stable, which makes some people like that. Arch is very developer-oriented. I actually recommend you guys try Arch. It’s definitely good. It just can be a little strange for most people though. I guess the difference between the Arch packaging methodology and the more familiar Ubuntu Software Store and apt package manager can account for this. The rolling release method of software distribution constantly updates the system to the latest versions of the software packages, but this may not always be the best way to run a system, you may wish to delay an update on certain packages. But if a solid reliable server was the desired use case for the system, you would use Fedora Core instead. That is far more reliable than a constantly updated ARch system. But if the user wants to try bleeding-edge software then Arch could be a good contender. Yes. I just tried it. I do have a lot of distro-hopping experience, though, so I am quite familiar with them.
That said, Arch has its merits (such as the great documentation and the user-friendliness of the packages management), but personally, I would not install it if I had not been on a mission for speed (something I would still try if I didn’t have a time restriction). It’s not that Arch is unstable; it’s simply that it takes a long time to install or upgrade, the result is that it doesn’t always feel as user-friendly as other distros. As far as other options go, the Ubuntu servers seem to be more mature, well-thought-out, and easier to use than those of Arch, and they are free. Personally, I wouldn’t use the latter if I had money to spare, or didn’t mind time spent on installation and configuration.