This is a good question. I know my way around an Arch box pretty well. I love it, but that doesn't mean its for everyone.. Like VPR3 said, you may not like it if you're not familiar with a terminal. A fresh installation of Arch is completely bare. There is no deskop environment installed, which is a huge turnoff for beginners. You will have to do a lot, I mean a lot. Its frustrating at times. And just a pain in the ass. But it will teach you a lot. You'll be referencing Google a lot, troubleshooting a lot, and furiously throwing your mouse a lot. But if you're really dedicated, you'll learn a lot. Also, its completely customizable. You like something? Install it, configure it. You don't like something? Don't install it.
My advice, install it next to Ubuntu. That way you have both. Give it maybe 60ish gigs for you to mess around with. But if you've never partitioned a disk with terminal tools, you may need a tutoria ready so you don't mess everything up. After its installed, just mess around a bit.