Do you think Tony was the triggerman in the death of Jack Masserone? I sure doubt it. Sure, he certainly gave the order. But he didn't do it himself. He's a boss, and that's a piece of work he would delegate to an underling, no doubt about it. He wouldn't take the risk of getting caught or being successfully linked to a murder by the cops and Feds. He'd give the order.

Tony killed Febby Petrulio (in the "College" episode) because he was the only one around to do it, and he thought that Febby might go on the lam any time if he hesitated.

And Tony personally killed Big Pussy because that whole affair was something that affected him deeply. It wasn't just some rat, this was one of his very best friends betraying him.

So, as it stands, Silvio is beating Tony 3 to 2 in the "rat-killing race"!