Hmm, I had no need for the programming additions in LuaTeX; my main concern was using UTF-8 and having better integration between LaTeX and my system fonts. XeLaTeX offers a great out-of-the-box experience for using commercial, "pro" fonts, particularly on a Mac; check out the 'fontspec' package. However, I've heard the LuaTeX can do microtypography really nicely, and I haven't checked if they've made using system fonts easier, so maybe it's work a second look.

There is a beta 'microtype' package for XeTeX but it doesn't have all the features that LuaTeX has (font expansion?).