I will not go into details, but I would like to hear your opinions about this:

Essentially, my project will be a 2d game, with lots of complex levels, where some might be simple and others might be a bit more deep, with physics, etc. We want to implement our very own online structure: logging in, leaderboards, achievements, friends etc with our own servers. This means no OpenFeint nor GameCenter at all. We expect this game to be very large in both graphics and audio. We wish to use in-app purchases.

Now, we considered two options. Cocos2d and Unity3d.

We need help deciding using the factors I mentioned before (networking, good performance even for a large game in terms of graphics and audio like this, in-app purchases, etc) which option would fit better this?

Technically, both options can create 2d games. I'd like to hear your opinion.