Scarpa. Hands down. He burnt 3 bosses, provided the PC for the Commission case, and passed off information for more than 30 year. Most of Valachi's info and testimony came from Greg Scarpa's 302s that had been going to Hoover a few years before Valachi was on radar.
If I remember correctly, Scarpa was THE FIRST informant EVER for the FBI. Guys had rolled and testified in cases before connected to OC, obviously, but usually only in cases that they were involved in, and on their co-dee's. Scarpa's intel is actually what got Hoover to actually admit that there was indeed a "LA" Cosa Nostra operating in America.
Some of Valachi's answer might have come from Scarpa. Scarpa became a snitch around the same time Valachi flipped. Valachi had been a made man for 30 years, while Scarpa had been made for around 5 years. He fought in the Castellammarese War and was a made man when Scarpa was wearing diapers. As far as Scarpa being the first snitch, that is likely not true. I'm sure there were dry snitches even back in the 1920's. He obviously did alot of damage during those 30 years, but those photos were only a small part of the evidence that put the bosses away. The wiretaps were the bulk of the evidence. Without the wiretaps, all they had was a bunch of photos of old men going into and out of a house.
Have you read Deal with the devil? Lance Breaks it down pretty good on the whole issue. Scarpa gave the entire structure of the families, around a year prior to Valachi coming out, per the FBI's own documentation. Scarpa was responsible for the Colombo family downfall. He inadvertently helped get Persico in as the boss, set up anyone who he viewed as a rival, just destroyed that family. Also they would not of been able to get the wiretaps without the information that Scarpa had provided in the commission's case.
Like others have said, it's not like he flipped and gave a one time testimony of inside information. This guy had 30 years of doing nickel and dime shit, but it added up. He fucked over generations of gangsters. The entire blueprint of what the feds used for the mafia in new york was provided by Scarpa in 1962 at the very latest.
