I've used InVision a lot in the past and liked it quite a bit. That said, it's certainly not without problems. There are small, annoying bugs everywhere. The UI is a little bit annoying. The fit and finish just isn't quite where I'd like it to be.
Marvel, on the other hand, seems to do everything just a little bit better. I've started using it more recently and I really like what I'm seeing. Everything appears to be well-polished. The UI is a little bit nicer. And it has the ability to directly create wires within the tool itself, which is great at the early stages of a screen design.
Why do you think InVision is the incumbent? Those of you who prefer InVision, why? Do you guys have another favorite?