Glasspack. Sixes sound weird to me with a chambered muffler, but you can't go wrong with a good ol' Cherry Bomb.
I run a Cherry Bomb Chambered Muffler I also have a flowmaster 40 series on it, it sounds identical to the Cherry Bomb turbo II muffler...that was a pleasant surprise.
im with all of them cherrybomb glasspacks are the way to go. i have a 302 with duel glasspacks and they are awesome and ive heard them on 6 bangers and they are amazing too