They have different characteristics. What looks better is personal preference.
3D Vision brings things to life with full binocular vision. That means a lot more to me. Not everyone seems to care about 3D, or gets sick/headaches from it. With the Helix mods, over half my games support 3D well. Most the biggest blockbusters these days have it built in (Crysis 2 & 3, BF3 & 4, Metro 2033 & LL, Tomb Raider...).
120hz makes things feel responsive and smoother, but 1440p gives higher definition and usually better color production.