We have 2 sites, 1 on clickbank, and a different unrelated site on Shareasale.

We just did a launch on the clickbank site and it was MUCH easier to get affiliates and partners involved, simply because everyone already has an account, knows the systems, trusts they will get paid, and it is just really easy for them to copy and paste and get involved very quickly.

For this reason, especially as it sounds like your first time, I would recommend using clickbank. If it is a success and you want to move to another in the future you will have some partners from this to contact and let them know, and at least you know the JV / launch process a little better and what will be required from another network or your own solution.
Dan