If you are talking "complete" lowers it is hard to say. Just buy what is affordable for parts. EVERYBODY has their favorite.You could ask the question about the just about the stock, as that is the one part that you get for fit, function, and comfort. I personally have a RRA, Spikes, and 2 SAA lowers. RRA 2 stage trigger, 2 Del-Ton, and one Spikes LPK. A Tapco 6 position CAR stock, A2 standard stock, and a RRA pistol buffer tube. Spikes, Del-Ton, and RRA CAR, H, and H2 buffers. It is all about performance vs. price and vice-versa in some cases. I like them all. Just be forewarned you will probably end up with a few spare parts. Thats OK, you just use them for your next build I would search here and on ARFCOM for the individual part and make your choice from that info. Then comes the hard part, the upper parts and optics.