I had some decent kicker's in my GP, 6x9's and 5 and 1/4. This was a few years ago so I dont remember model numbers.

My dad had Infinity speakers in his GP and they sounded much better.

Most of this is preference tho, what one person thinks sounds "good" or "reasonable" may sound way different to your ear. Try going to local electronic stores and listening to speakers to decide what you like.