I'm going to assume that since you're asking you probably aren't after a tiling wm... yet
Have you used Linux before? If not then i'd stick to Gnome, KDE or XFCE just to get used to how things work. You could try LXDE or Openbox (i think a lot of Archers go with that) but i didn't really get on with it personally. Gnome can be good, but it's taken a bit of a weird turn of late. Depends on your tastes i guess. KDE is probably the most resource intensive, but you wouldn't have a problem with that. I've heard a lot of good things about 4.8 so it's definitely worth considering. XFCE is the lightest of the three, but will take a little more effort to get it looking nice. It's defaults are pretty rubbish