I have Koni STR.T shocks and struts, I combined them with H&R Super Sport lowering springs, and it is a HUGE improvement over stock (my old shocks and struts were completely shot though). I did some research and was thinking about getting KYB because they were cheap and I had a tight budget, but after reading reviews and comparisons, I ended up spending the extra dollars to get Koni instead, seems like just about everyone would agree they are better than KYB. I would get Bilsteins, but that was too expensive this time. Most people recommend to not get new quad-shocks when you get better-than-stock shocks, especially if you have aftermarket control arms, as they are not necessary anymore then.
2003 Mustang GT
Intake & Exhaust: K&N FIPK CAI, Mac O/R H-Pipe, Custom Catback w/ Magnaflow Magnapack Mufflers.
Suspension: H&R Super Sport Springs, KONI STR.T Shocks & Struts, J&M Caster Camber Plates, Steeda Bumpsteer Kit, UPR Elite LCA's & UCA's.
Performance: BAMA 93R Custom Tune, FRPP 4.10 Gears w/ Terminator spec T-Lok.
Planned Mods: FLSFC, Eibach Sway Bars, Throttle Body, Plenum, Rims.