I went Ubuntu -> Crunchbang (r.i.p.) -> Arch, with a short stint trying out Gentoo. Arch is my favorite, but that is largely because I am a control freak when it comes to my system.
Ubuntu is nice if you have never used Linux. There is a wealth of resources out there that assume you are using Ubuntu for your distro, it offers a lot of default options that let you do things without worrying about them (like network configurations or mounting of file systems), and it is incredibly stable. However, changing or removing certain aspects can prove difficult. If you start to deviate from the things they give you, or the things available in the Ubuntu app marketplace (or whatever it is now), then you will probably experience some friction. Or, if you are a developer and want to run with the latest updates for that compiler that made it finally not terrible, you are going to be waiting a while until it moves into the ubuntu-stable repository (and mixing experimental/testing/stable is risky, if you aren't sure what you're doing).
Arch is the other side of that coin. If you want something that just got released, Arch will probably have it, either in the standard repos, or the AUR. And pacman/yaourt are some of the best package managers I have used. And making changes to your system is easy, as there is very little that gets in your way (systemd is perhaps the only thing to worry about). And for any changes you do want to make, the Arch Wiki is an absolutely fantastic resource (this is true in general, for most distros). All this comes with a price, as you have to manually do a lot of stuff. You have to install your window manager or desktop environment; you have to manage or set up your network connections (and there are a few programs to choose from); you have to write your own xinitrc (if you want), set up your session manage, everything. A base Arch install gives you the coreutils, and little else. For some people, who want to control everything their computer does for one reason or another, this is perfect. For others, this is maddening (I assume).
Most distros exist somewhere on that spectrum of usability and control, with Ubuntu on one end and Arch (and to a further extent, Gentoo) on the other. I have spent hours upon hours learning about my system and what I can do with/to it using Arch. It is fun for me, but I don't think that is for everybody. Its up to you to decide what you want.
(Protip: install to a virtual machine or a throwaway machine before making the full switch. Even with Ubuntu its much easier to break your system than Windows or OS X)