any suggestions?

 

straight pipe

 

With absolutely no other info given, I'd say neither. A resonator/presilencer will sound better than a straight pipe and not be deafening. And it will flow better than a cat. It looks like you're in Wisconsin, so you probably don't have to worry about smog testing.

 

Pre-silencer

EDIT: ^ arg beat me to it

 

I won.

 

high flow straight pipe

 

Low flow bent pipe? high flow straight cat? low flow bent cat?

Couldn't help but inject bad humor.