A free-floated barrel typically improves accuracy, at least in the AR platform, so if you're looking for really small groups then it's worth focusing on.
The RRA LAR-8 took several years of engineering for RRA to make work right, in large part because of the use of FN-FAL mags that were, at the time it began, cheap. They are no longer cheap or abundant. They are a quality mag, durable, no issues with them, but the supply is drying up and like-new FAL mags are in the $20 range now, and likely higher in the near future. Worn used FAL mags, still serviceable, can often be found for $10-15 or so. The FAL mag was intended to be a strength of that design but has really turned out to be a drawback.
Armalite quality is great in my view, but nothing wrong with RRA. I think you would find the Armalite very slightly nicer than the RRA and its customer service noticeably better (more responsive, at least), but both are good companies.
M1As are readily available if that's what you would rather have. In fact, much easier to find than the RRA LAR-8 most of the time. I would decide what you really want and not default to something because of perceived availability issues.
Armalite and Springfield Armory (M1A) have lifetime warranties and excellent service. DPMS has only a 3-year warranty though they do seem to have an excellent reputation for service within that time frame. Not sure of the RRA warranty. I really wanted a LAR-8 several years ago but really got soured on RRA after not being able to get through on the phone after perhaps a dozen attempts spread over several months, and this was long before Obama was even a candidate. They didn't reply to email (back then) either, though that's more common. However, Armalite has always replied to my emails promptly with useful replies written be someone who seems to know what they're talking about. (I have emailed a mix of questions, some relating to an AR-15 I own, others relating to potential purchases.)