It's been 'round a year and half. But, eh... never mind.
I guess Big Smoke and Billy Grey are heading this title. In my opinion, Billy's betrayal was the biggest one and most heartbreaking one; just like Smoke to CJ and Sweet, Billy was a childhood friend of Klebitz, Jim, Angus, Terry, Clay, and Jason, his bike was built by Johnny, Jim and Angus (as far as I remember), they were in The Lost MC for many years, they spent most of their childhood and teenage together. What even makes the betrayal worse is when Billy says "You're my brother, Johnny. Always", then know that the Triads' ambush was planned by Billy, requested the Triad boy to execute Johnny and Jim, watching Billy has already crashed the bike that was built by his childhood friends, shouting "You set me up, Johnny! You set me up. You're dead! You're dead!" just to start a civil war inside the MC, blaming Johnny in tries of getting him killed. And then he sells The Lost out by selling information for the FIB, so that they can take the MC out. (noting that just recently he was still the president of it, for a couple of years I suppose)