I would say mint unless you really like Unity. Otherwise, mint has a less nonsensical approach to handling new concepts. LMDE would be even better.
If you've used linux before, maybe you could try Debian. The installation process is about as simple as Mint's nowadays. Ubuntu has simplified their installer to the point of being fully automated, though, so if you really hate the initial install, go with it. (Win XP's was harder than Debian's is now though

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The only complaint I have with debian right now is that the testing version is only about 2 months old, so there are hundreds of updates all the time. The system isn't unstable, but it's kind of annoying, especially considering how often kernel modules are updated, which requires a restart. Mint (not LMDE) and Ubuntu won't have this problem: They'll have 300 updates right after installing, and then a slow trickle until the next release comes out.
Also, Mint won't use Gnome Shell, which is about as bloaty as KDE4 was when it first came out. It will use the improved gdm3 system, though, just with the classic Gnome Desktop. Ubuntu, I believe, has its own desktop manager specifically for unity.
Oh, and it's good to move away from Wubi, regardless of your decision. It causes all sorts of issues, like not having swap, so running out of memory crashes your system.