Nigeria isn't the strongest county in Africa continent neither are the weakest. When it comes to AFCON competition, Egypt are the strongest after winning it a record number of seven and even won it for three years straight (if I'm not mistaking). For world cup competition, Senegal has gone the farest more than any other African nation. The highest Nigeria has gone is the round of sixteen which they usually end up getting knockout by Argentina.
In the knockout qualifiers Nigeria wasn't the strongest opponent, Ghana has a number against Nigeria. In all their head to head meetings, Ghana has the highest number of win as they always found a win to win Nigeria so their win wasn't a surprised as well.
I thought Algeria was the strongest along with Egypt? I know that they were the top 2 favorites in the last Afcon tournament, even though Senegal won it, and also qualified for World Cup at the expense of Egypt, but they were only 3rd or 4th favorite.
Algeria really really disappointed a lot of people (including me) so I do remember them being top, and had some magnificent players in Europe as Riyad Mahrez comes to mind.