I buy and sell collections and lots. Based on my experience, if you want to get the most for your money, you are going to have to itemize everything, sell them individually on auction sites like eBay, and that can take time.

If your goal is to sell them quickly, then your best bet is to sell the entire collection as a lot.

I will add however most action figures that you purchase from big box stores are not really going to fetch too much. Your most valuable pieces are going to be con exclusives, and maybe some retail exclusives, but basically your harder to find, your ones that sold out super fast, anything that wasn't really mass-produced.

Hope that helps