Any reason to select one brand over the other?

No, I think if price is the same it comes down to personal preference.

What configuration are you looking for?

I have a Bushmaster 20" standard A2 and just purchased a new Armalite Competition model.  The Bushy has a slight barrel index problem causing my rear sight to be about 10 clicks off center to get zero.  The one item I liked about the Armalite is that the front sight is "clamped" on with allen head screws.  These screws can be loosened and the sight adjusted to that your rear sight can be zeroed in center.  The only other issue I have with the Bushmaster is that the mag well is tight enough that not all magazines (especially the mag that came with the rifle) will not fit well.

Other than that (these are obviously minor issues), the Bushmaster is a fine rifle.  I shot my first NRA Highpower match with it (remember it is just a standard A2) and shot a 754-11x out of a 800 pt. aggregate.  Not bad.