Which OS / package manager ( if any ), or how will you plan to install it? ( "Path"/"ENV" spelling suggest suggest windows, but not sure ). I mean because it depends on that. My debian lists lua 5.2/3/4 and luajit (5.1, luajit 2) w/o conflicts among them ( not the latest version, but for a newcomer I would recommend that in it ).
FWIW, as I only use lua embeded in my projects I routine compile it, link it into my favorite $PATH directory and it works fine ( I do use command line lua to run tests in the modules which can work outside the host or use some dummies ), but luarocks and cousins may be a little more difficult if you plan in using them.