Hmmm....
Bushmaster has the biggest name recognition. When I tried to sell a kit-gun at a gunshow last year, of the 150 different people that came up to me or handled it, 149 asked if it was a Bushmaster! (not exact numbers, but it was truly, totally overwhelming)
So, if you plan on easy resale and decent value, the Bushmaster is king. Most people interested equate AR-15's with Bushmaster.
RRA is better from a different perspective. Their 2-stage trigger is absolutely worth it. RRA is gaining a huge following and is growing in name recognition. The word on the street is that RRA is associated with "tight" or "accurate" or "quality" AR's. That's all I hear outside of the web, and the web is crawling with RRA lovers.
Armalite has a very interesting lineup these days with midlengths. Armalite is also very high quality. They don't seem to be getting much of the spotlight due to RRA, but they're a good choice too.