The only really credible testing is VADA because it is random and not at the whims of the fighters and promoters. USADA, for example, has made bizarre exceptions and courted the scheduling made by the fighter. Under these circumstances, someone could be cheating but being tested only when they won't get caught and are therefore "innocent". If you are mentioning the Mayweather-Pacquiao fight, then it's worth mentioning that Mayweather wanted to use USADA which basically means he can look like a proponent of clean testing, but knows how to use USADA for himself. There have been numerous instances where USADA started or stopped testing at a fighter's request. Mayweather failed three A sides under USADA but that gets hushed up. USADA granted "inadvertent use waivers" on three separate occasions meaning, if you cheat you won't get caught.
So why does Mayweather get some immunity here?
They didn't even look at his B samples. Now, Pacquiao, ironically, has not failed any A samples but people are accusing him of PED's, when, even under a shoddy USADA system, Mayweather is still looking suspicious. If one looks suspect, why not the other? If Mayweather really cared about clean testing, he would have used VADA. It catches people. They caught Canelo, and A sides of that level cheating don't often get caught.
Either way, I really try to give guys the innocent until proven guilty (even with the above, I try to think that Mayweather and Pacquiao are cleaner than others because at least they did some testing, but it's really empty optimism, isn't it?), because anything past that is speculation, but it's really hard to see people accuse Manny but not accuse Floyd. If you are using VADA all the time like Donaire or GGG, then you are on the safer side, if you are using USADA it means you want to legitimize your cheating or mask it altogether. There are some extenuating exceptions, like the name Evan Fields in the steroid distributor's client index that happened to be a landline to Evander Holyfield's home phone number. That was shifty.
