well this really is based on few things:
What materials will you need and does Cycles support those right now?
What is your PC you render on and how long will the animation be?
Will it be indoor or outdoor?
Will you need/use compositing/render layers?
In the past weeks I gave Cycles few tries again and noticed that to reach a finale rendering for my product design the interactive preview is drastically shortening the shot development and I only work on a dual core laptop, so I dont have a GPU to render with.
I work with a lot of glossy materials and Cycles simply makes short work out of them putting BI’s raytracer where it belongs to, the trash can because it is unusably slow with layered and complex materials.
In Terms if composition Cycles clearly reached a mature level with render layers, excluding objects from affecting specular diffuse and camera. It also offers AO now.
Yafaray on the otherside is a pretty well developed render engine as well with great materials and quite fast render speeds.
But it does not offer the interactive rendering nor a good connection to compositing.
I think considering that Blender is currently using Cycles for the next movie project I am close to suggest that maybe considering Cycles, even more when you have a decent PC and a good GPU.
The per shot render might be longer on complex scenes but the shot setup time is drastically shorter with Cycles.