Ive Heard alot of interesting theories but this is what I believe

It is not
Patrick Jane
Van Pelt
Rigsby
Ray Haffner (too obvious after red barn)

However I also believe that season five wont get us anywhere closer to finding red john, The name isnt on the list the options are too open and he has confessed to missing some people and it has to be after his wife died.

All I hope is that this doesnt end like lost and Patrick Jane is actually delusional and this never happened. So Heller if you read this do not end it like that, I will be extremely pissed off.