This is tough. For roughly 19 years it was the Prince Triple Threat Hornet, 2001 (red) model. It had power, control, feel, and I served well with it. But when I started with a coach, and really tried to improve my volleys, it would "sag" a bit with prolonged net play. I flirted with the Phantoms (best volleys, could not serve with it) for a couple years and now I think the ATS Tour 100, 290g will be the all timer. It does absolutely everything well.
Single best serving racquet was the original TT Hornet, black version. I tell it to serve and it flips around my wrist like a mousetrap firing. But the ATS Tour comes close to the Hornet red version.
I still keep the Hornets and a POG in my bag for fun.