I'm gonna end up going against the grain here, lol. For me it was;
1: Jake. I like his gameplay the best (there's just something viscerally satisfying about beating a final boss down with your bare hands), and I liked the RE3-style pacing of his campaign, being pursued by the Usatank. The only thing I DIDN'T like about his campaign was the ****ing motorcycle chase in China. ****ing cheap-ass deaths galore.
2: Leon. The atmosphere of his campaign reminded me of RE1/RE2, which was a welcome change from RE5 and RE4, and the little bit of puzzle solving in the campaign was fun to see again.
3: Chris. His story had the most character development, and the weapons he gets during his campaign were the most fun to use.
4: Ada. I only put her at the bottom because, while I'm not very far into her campaign yet (I literally just finished her prologue last night), her limited weaponry made it really hard to get through some of the areas, particularly once the sub started sinking, and there were all of the Gnezedo infesting the area I had to work my way through with a fairly limited amount of shotgun ammunition. I like the puzzles, however, and her grapple gun.
"It takes a real man to fight with a giant pink scythe." - danstu
Chris, I've heard from lots of people say his story was best and I went into Chris's story thinking nothing was going to top Leon's. Hell, I went into Chris's second chapter thinking nothing was going to top Leon's. But it REALLY pulled through. Chris's VA did an amazing job on everything. I used to hate Chris since he went all bulky, but RE6 really made me like him. He really got personality this time around and his story was the best in the game. Including some of the most emotional scenes.
Jake, I like both Jake and Sherry, loved the story and Ustanak and the gameplay. It was pretty consistent with story quality and didn't really drop off at any point and had a pretty good ending. A lot of it was cheesy, but I felt that was the charm of it.
Leon, but barely behind Jake's. Leon's story kinda dropped off near the end, but overall it was well done.
I haven't finished Ada's yet, just started playing it and I want to reserve judgement until after I've finished.
You should check out Imagine Dragons http://youtu.be/wO0ohGn-x3E <o> YES! \o/ <o> YES! \o/ <o> YES! \o/