I'm going to say Him, also finding an infintie lava lake right next to an infinite water spring.
Herobrine is NOT GOING TO BE PUT IN THE GAME. Notch said this multiple times. If he'd put some creepy ghost in the game, he would lose alot, and I mean SHITLOADS of players, and the game wouldn't sell so great either.
The concept of the game is that you mine, and you've got some exploding mobs. If he'd put in Herobrine, he'd screw up the entire game.
Also, there aint no thing like an infinite lava thing. Besides, ain't rare to find lava lake and water lake next to eachother, as water lakes are everywhere.
While many groups disagree over Herobrine's existence, the majority opinion is that he does not exist. Although an entity like Herobrine may very well appear in Minecraft due to the prank, and likely when it is least expected.
It would be nice to have a bigfoot like thing in minecraft, like he wouldnt hurt you, but once in a while you'll see him watching you. Like hes curious.
if i saw a bigfoot,i would be all like ZOMG WAT IS DAT and try to kill it.