I'd pass on the poly lowers. It dont take to much pressure to snap one.
A lowers a lower... not to many out of spec lowers floating around today and even the cheapest of lowers will perform just as well as a more expensive model if its in spec.
However, I would avoid any of the "local brands" no clue how good they are and you have to think that the hand full of people who recomend them are probably buying them because there the dirt cheapest and they have no real experiance with the platform or the financial backing to shoot one until it fails. They may be the best thing out there...there probably not. I know of one local machine shop producing 10 rifles a week. Right now there 75+ rifles backordered and they are selling for $850 IIRC for a complete rifle. I've got a friend whos drinking there coolaid but I'm not going to waste any money preordering what's probably junk just yet.
I'd stick with a established brand RRA, Bushmaster, DPMS.... ect ect ect... There all gona be about the same when it comes to lowers.