Costar's shouldn't ping (ping == the sound of the switch spring)
If you don't lube them, they clink a bit, when you lube them, they're the best stabilisers, imo
The stabilizer might be hitting the key itself, in that case you need to sand the inside of the key a bit, or lube the middle of the stabilizer wire, or just push the stabilizer construct further a bit
You can change keycaps on cherry's easier, yet if the keycaps are loose a bit, you can't easily put a sheet in between the stabiliser inserts, you can easily do this with Costar's, so imo, Costar >> Cherry
Also the pings obviously come from the switches themselves, so it's just luck getting a set of switches that doesn't ping, unless the factories segment and eliminate switches beforehand, however this seems not to be the case, unless you mod the switches, they ping, I'm unsure how KUL keyboards don't ping, almost all switches ping, you can easily hear them on Clear's/Green's
The WASD stabilisers also fall down from some of the keycaps, yet you can easily put something in between and make them stay, you can't do this with Cherry's, it would be near impossible
Long story short, imo, none of the keyboards are perfect, choose your set of caveats :)