I just got a 2000 bonneville SE and was wondering a few things. I'm planning on a fenderwell intake, magnaflow hi-flow cat, a 180 thermostat, and a hi flow muffler. Here'* the question I was thinking of running a crossflow muffler( camaro) style with tips on both sides
or should I just run a single in single out muffler with 1 type like stock? Does it make a difference in power or sound? I thinking magnaflow because I don't want it to sound raspy.
any help is appreciated.

power, no. you wont be getting any power at all from the aftermarket muffler vs. stock. That mod will be sound only.

then which will sound better, louder a crossflow or just a single in single out?

on my n/a im running a dynomax super turbo and for power from the exhaust don't forget the downpipe