What is the most effective athletes foot medication cream or spray? Is generic fine to buy?

Both will work. Most topicals, whether cream or spray, will work if used as directed. Generic is fine. The key is to use regularly to get the best results.
Generic is fine. I believe cream are better than spray because of direct contact to the skin. I think the most effective over the counter cream is lamisil (terbinafine). There are also many prescription meds if this does not work.