Manjaro isn't really useful if you already run Arch with no problems. If there's a specific feature it has, like the graphical pacman frontend, then you can always just install that on normal Arch Linux.
Manjaro tries to be Ubuntu with Arch, in that it packages up simplification tools so that it's easier for non-linux people to use. My few moans with it are the desktop environments available to choose from (which is fine, they're easy to change, but it's packaging high weight environments, which I personally am not a fan of), their using separate repos for packages (somewhat understandable, as Arch has strict guidelines as to what ends up on their repos), and just not lining up with my personal theory that Linux is best used when you understand how it works, not when you're relying on someone else to understand how it works.
I obviously use Arch, and I think it's one of the best Linux distros for people who want to learn Linux. It has one of the best implementations of modularity in the Linux world, with an efficient and pretty hard to screw up package manager (let's not talk about the AUR though). It has better out of the box hardware support than most other distributions, given that it does not come with X, and the Linux kernel supports terminal modes going back to pre-VESA BIOS modes if you really needed it. This means it's possible to better understand your hardware and get the right drivers while you're installing X. It encourages people to keep it simple, stupid, and understand how your machine works so you can get the best out of it.
In my opinion the only possible switch I would make is to FreeBSD, which has much cleaner implementations of a lot of things, and it already runs on my server. Its only sin is that it has no usable linux binary support (doesn't support latest glibc). If it did, I'd love to have hybrid pacman/pkg package management (or both in the style of PacBSD) for Linux/BSD binary package management. If I can get all my Linux stuff, and all of my BSD stuff in one place, I would be in heaven.