cj have material products you may choose, cb only accept digital products and mostly offer very high rate commission for the products are digital.
There are a lot of differences. You can chose to use both of these two networks and there be no harm at all! The main difference is that CB majors in digital products whereas CJ has both Digital and Tangible Products. Hope that helps.
Clickbank have far more products and you can use different techniques like I do to make stacks of money. =D
Clickbank is known for digital products whereas CJ is more popular for its brand value. (It is a big marketplace for physical goods).