Sway bars?
 

Been looking into getting some of these as the reviews I've read say they make a night and day difference, but yesterday I got underneath my s550 and noticed I already have them and they look factory. So how could new ones make that much of a difference?

Well sway bars come from the factory for pretty much any car on the road. The aftermarket is talking about stiffer and thicker bars to reduce flex and make it handle sharper. I suggest doing a good amount of research into these and asses what goals you have for your car. Stiffer bars with improve handling but if they are too stiff or not well chosen along with other suspension mods they can upset the balance and make you understeer or oversteer worse.

They can make a good bit of difference. Im not so sure about the S550s, but with the S197s quality sets of springs and shocks/struts make a more significant difference in handling and gave you a much better ride as well. Just something to consider.

I was looking at the steeda's because quite frankly everything else I have is steeda lol. I've heard guys run stock suspension and just add some new sway bars and it's great. Was just wondering if you guys had any experience

I did shocks, springs, and lcas first. The difference was night and day. I only changed my sways because the rear sway developed a squeak in the sway bar mount. I gained adjustability that allowed me to fine tune the handling a little. It was better but I wouldn't say it was as huge a difference as the shocks and springs. The springs and shocks totally changed the cars driving personality. The sways made it feel a little tighter in the turns. Upgrading my tires made a bigger difference than sways.