While I'm naming Partridge as the ORIGINAL Red John, the truth is actually twofold...

Brett Partridge USED TO BE Red John. Bruno Heller has originally planned to have him as "just this simple man", to quote him, and has given too many clues to his identity. It was spoiled too early, and now he's had to change it.

Brett was John. Who is John now? Nobody. Bruce Heller doesn't know yet. Who is he going to be? We'll see at the end of the series and not before.

Bruno Heller still hasn't decided who Red John is going to be. 

After everyone figured out his originally planned identity in Season 2 (some already in Season 1, after his character has been prominently placed next to Jane in the early promo posters), he's been egged and has switched strategies. Instead of being too self-congratulatory with giving out actual clues (which is why the original identity was spoiled so early), he's been backtracking ever since, planting tons of new fake "clues" everywhere he can, in hope of making every viewer suspect every character in the series. 

It's working for about 95% of the viewers, Bruno's happy, and he'll be milking the red cow until cancellation is imminent. Then, with the hundreds of false clues that have been planted, he'll be able to pick literally anyone he wants, even at random (though most likely after checking the Mentalist wikia for current fan favorites), say "there, s/he's been Red John all along!" and point to whichever "clue" he wants as "proof". 

Decent plan, which will probably work, and whoever he picks up for Red John will hopefully be satisfying. The show is still strong, nothing about it has been destroyed so far (unlike, say, "Dexter", blown up by the atrocity known as "Season 7"), and it will probably stay decent with Bruno Heller helming it (again, with "Dexter", it was the change of runners in Season 6 that destroyed the series). It's just a bit of a shame that he's so concerned with that trap he found himself in. Red John has grown into a monster, the whole series is about him, and without him/her, the series will fizzle out in 5 episodes - which Bruno Heller knows, and which is why he won't pick the "revelation" until the cancellation. 

Frankly, I'd hope he'd return to the original identity, but that's past - he's accidentally made the character from what used to be his original roots (just a clever serial killer, operating alone or with a tiny group of accomplices) into this giant mythical Satan-like being with 5000 devoted johnologists standing by, and by now he probably feels that he'll need someone much bigger to fill those shoes. (Perhaps that's why a certain "bloke" from Yorkshire has been returning so often, though hopefully not.) 

Unless he brings back the original RJ from Season 1/2 and retcons him into someone bigger. But that would be too obvious.