Xubuntu (forgot which version, probably 12.04) and Kubuntu 12.10: Neither do the job.
OpenSUSE: Never got to test it on multi monitors actually. Plus I'm really not used to the different commands.
Xfce's display tools are really primitive, and the command line, randr, needs to be used to get the monitors configured. The display configuration tool is the one thing that they really need to work on. Otherwise, it's one of the easiest DE to work with. The small Xfce team has put a lot of thought into it, and it shows.
Suse is kind of an oddball out of the Big 4 distros. It's an excellent desktop distro thought.
Looks like Mint's a great distro to settle in, but that's also hard to say when I've only used it for about an hour. (Although if I liked it that much after such short usage, why not?)
Cinnamon is a nice window manager. I have a spare laptop at work that I keep Mint on. It's not the speediest thing, but Cinnamon runs rather well and looks good.
The laptop has a Broadcom WNIC, and I didn't want to spend the time getting the drivers running under Fedora.
KDE is also not picking up the super key (Windows icon key) out of the box, while Cinnamon is.
KDE recognizes the Win key, but it doesn't have the key assigned to anything by default.
If you want to try KDE, check out OpenSUSE or Fedora/Korora. Kubuntu is considered to have one of the worst KDE implementations.
My Linux box at work runs RHEL+KDE and two monitors and it just worked out of the box, maybe give Fedora or CentOS a try.
Fedora handles multiple monitors really well out of the box. It's one of the reason's I've really stuck with Fedora.
I haven't tried RHEL/CentOS/SL outside of a server setting, so I can't really comment on how well they handle it.