I like a high flow cat paired with a resonated and muffled exhaust for that almost-stock-until-stepped-on sound. Other folks like straight pipes all the way back.
unless youre buying it out of some dudes van, any downpipe will be reliable and last. They arent a working mechanical piece of machinery it is literally a pipe of steel.
the only real differences between brands will be fitment and thickness of the steel. the cheapest downpipes will sound more tinny due to thin metal while the more expensive ones will sounds a little deeper due to thicker metal