This is a pretty clear victory for Trunks imo. Cell seemed to pay more attention to him than Piccolo:
Cell: “It’s the same thing. Vegeta and Trunks may have raised their power, but they should still be inferior to you…â€
Cell (to Gohan): “If you don’t show your true worth soon, things will go past the point of no return. Look closely. Vegeta or Trunks are barely fighting evenly…Even Son Goku is in trouble, having lost his stamina…â€
And if Trunks is still close to Vegeta, which those quotes would suggest, then he's in a range of power that until Goku uses his full power, is the best chance of beating Cell (as far as Vegeta is concerned), while Piccolo knows he has no chance as soon as he leaves the time chamber.
There's also this:
Vegeta: “…That’d just be a waste of time. Only Saiyans can step into the region ahead…â€
But it may have just been empty boasting, who knows.