I've heard a full jardine, and a yoshi-slip on so far. Both sound pretty good, although I liked the jardine more. Definitely way better than stock! I know the yoshi is cheaper, and just changes the sound. The jardine (and all full systems) cost more, but they also increase (or decrease) horsepower. So I guess it depends: slip-on just to change sound, full-system for a power change (it doesn't make a huge difference, but every little bit counts
)
Since the OP is just looking for a sound change, and at a cheaper price; a slip-on would be their best bet. If they want to have a relatively easy time putting it on, my recommendation is the yoshi. No hassle to install, and a decent price.
Although, I'm wonder what pipes not made specifically for the GS, but modded to fit onto a GS sound like.
I've got a pretty good idea for what I want to do with my bike once I streetfight it. Only problem is deciding what can I want to bash on it. I'll be able to smash pretty much any can (if all things work out okay, I'm planning on a custom exhaust pipe built for it.)
It's hard to find sound clips, and even then most are bad quality sadly. And since the GS is a twin cyl, it's going to sound way different than having the same can on a I4.