Linux Mint is Ubuntu-based. It has the Ubuntu installer and repositories, uses Synaptic manager, and the entire experience is very familiar to that of Ubuntu.
Just like Ubuntu, it uses the main desktop environments (excepting Unity): Gnome, KDE, Xfce and LXDE.
I have installed it with Xfce, which seems very light, not heavier than LXDE. Mint gives the impression of being more user-aware than even Ubuntu (or at least than the poor brothers of the Ubuntu family, Xubuntu and Lubuntu). I am under the impression that Linux Mint with LXDE or Xfce is more mature (out-of-the-box) than its Ubuntu counterparts. For example, Totem player seems a more complete and able player than I remember it in Lubuntu. But have not used Xubuntu for quite a while.