Personally, neither.
I would go with a S&W M&P 15 over either in that price range if possible. (Or Spikes if available)
Or I would save up a little more and get a Colt 6920. ($1,099 at my local Wal-mart)
But, given the choice between the 2 you have listed, I would go with the Sig. Just because I have had so much bad luck with the Bushmasters in the past, even before they got bought out by Cerberus. (when the quality was supposed to be better)