Leon's is actually my least played of the main three. It has the atmosphere, but it's too scripted to be consistently fun. I prefer fighting J'avo to zombies, as it seems the latter were brought back as a superficial way to please old-school fans. It worked for some, but I want the gameplay style of the originals to return, not necessarily the zombies.
I have a new respect for Jake's campaign as of late, and even though I despise Jake, I really like Sherry's character. The story is also fun in a cheesy, almost RE4-eqsue way. However, the vehicle sections and set piece events drag this one down a bit at times.
Chris's campaign has the best gameplay in my opinion. Few QTEs, two vehicle sections (one of which sucks but both are still better than the terrible ones in Jake's campaign), and the most non-scripted approach.
I thought I would love Ada's campaign the most since it was single-player only, but I think it's the weakest. There's no consistent theme; you just hop around from location to location with terrible pacing.
I played thru cmpaign 2-3 times for each character so far and I love all of them. They have their own style and I think Capcom did a good job on that.
Aside from Ada's, which felt like it was thrown together at the last minute, I agree with this. They all have their own unique flavors, and it really does feel like three separate games.