I've used a number of brands of .223 in my AR15, but mostly I've gone to strictly brass cases. I started out using the Wolf brand ammo, as it sold for $75 per 1,000, but it wreaked such havoc on my chamber I thought I'd never get all the varnish out! Had many stuck casings, and literally tore the rims off some cartridges when the extractor tried to pull stuck cases out! The steel Wolf cases are varnished to avoid rusting, and as the chamber gets hot, the varnish builds up, until the cases wont extract. Took a lot of work with brake cleaner, and a brush on a drill motor, before the gun would finally function normally again.
I now use either S. African, or Federal 55 gr ball ammo. Both shoot well, and with no malfunction problems.