That's odd. Usually most people but Leon's campaign at the top, and either Chris's or Ada's at the bottom. More so the latter is at the very bottom.
I thought Ada's campaign was generally well regarded?
Anyway, the reasons I place Chris's at the top is, among other reasons, is that it feels like the type of game Capcom actually wanted to make, whereas all the other campaigns are based on compromies with that original intent. For example, every character has the ability to take cover, even when it doesn't really make sense for them to do so (e.g. Leon). But if we look at Chris's campaign as a third person shooter, where the enemies happen to be monsters with guns, then what I'm left with is a campaign that's...okay. It's no Gears of War as far as TPS games go, but it gets the job done.
There's also the story aspect, that of all the campaigns, Chris's is the one that comes closes to an overall arch/theme, namely the whole 'soldier boy/band of brothers' thing going on. As themes go, it's generic, and I'd argue that it doesn't really execute it well (Chris loses his entire team in Edonia, then loses another team in China, but this time, he's fine with that...okay...), but it's something at least. It executes it better than the themes/arcs of Jake and Ada's campaigns.
So, yeah. RE6 is an example of "jack of all trades, master of none," and both the story and gameplay suffers for it, but Chris's campaign is the closest example of being all-rounded IMO. If I'm discussing the other campaigns, I like elements of Leon's (e.g. there's some genuinely good horror moments), but among other things, his game can't help but take detours into Stupidville (how many crashed busses, planes, and helicopters can he and Helena magically survive?), and while his campaign's story is the 'glue' that holds all the campaigns together, I'm still dealing with a weak plot overall. So, that leaves me with Ada's campaign (which is at least creative in areas, even if her character goes from 0 to 100 by the end), and Jake and Sherry, which fails to tell a compelling story despite having a great setup for it (two children of monsters) and a failed attempt at capturing Nemesis via the Ustanak.
So, yeah. I don't like RE6, but if I'm regarding it as a third person shooter, then Chris gives me the most bang for my buck.