I really can't speak as to which would be best for your country but I do know that ShareaSale is allowed in Nigeria and it's one of the top affiliate networks.
I have used them myself for many years and have always had good success with them. They have a wide variety of advertisers to choose from in just about any niche that you could want.
They are also real good at getting affiliate payments out to their affiliates on time every month which is something that we all like.
Here is the ShareaSale page that states that they accept Nigeria:
http://www.shareasale.com/international.cfm
Other than ShareaSale I am not sure who else to check for sure but you may want to look into Rakuten since they do have a lot of affiliates all around the world.