Newbie with the old question??
If I were to purchase a lower and upper separately to put together my first AR15
how would you rate the available lower and uppers in levels of quality.

Very Best
Best
Ok
Avoid

Thanks

You might want to provide more details about what it is you want us to rate?  There are a LOT of upper and lower configurations.  What are you wanting to build?  Carbine, middy, dissy, varmint gun?  What will you be using it for?  What is your price range?  You are probably going to get a bunch of different answers from different people.  My advise is to read, read, read.  Look through the tacked threads in the discussion and build forums, and use the search button to find info you are looking for.  Other than that, welcome to the board.  

Plus 1 to above.

avoid.

Nice lowers I have used personally:

DPMS
Eagle Arms (Armalite)
Cavalry Arms (a synthetic lower/buttstock assy)
Essential Arms

My latest builds have been with kits from J&T Distributing.  EXCELLENT!!!  Good components, excellent fit and finish (the upper comes completely built)