LuaTeX has some small differences from TeX that are not present in pdfTeX or XeTeX that I find really annoying. Most notably, it will not break lines after – or

LuaTeX has some small differences from TeX that are not present in pdfTeX or XeTeX that I find really annoying. Most notably, it will not break lines after – or — (whether entered as Unicode or with traditional TeX input using -- or ---). And the slowness is on pretty much all documents. It also does some weird mapping of character codes in generating the pdf files that should be invisible to most users but is evident if one digs into the output files. It could cause issues in malformed pdf readers although as far as I know this isn't an issue. Unless someone specifically needs Lua, it's hard to recommend LuaTeX over XeTeX.