Virtualbox first, to get the initial feel. Then live CD/USB to see how the distro works with your computer. It's a good way to find out if your distro of choice recognizes the hardware that it needs to. That way, if something is wrong, you can address it before committing to installing the OS.

I've tested Ubuntu (before they switched to the Unity interface), played a lot around Linux Mint, including dual booting. I ultimately settled on Manjaro. I do still occasionally test out other distros with virtual machines, such as Debian, Trisquel, and Zorin.