Without being more specific on what geographic region you want to serve, in terms of ISPs, it's hard to say.
For example:
If you look at submarine cable topology at layer 1, and BGP sessions, AS adjacencies between ISPs: Freetown, Sierra Leone and Monrovia, Liberia are suburbs of London, UK.
If you want to reach major things in the west african region the two best connected places are Accra, Ghana and Lagos, Nigeria.
On the other hand, if you put equipment topologically close to the cable landing station in Accra it will have rather poor connectivity to the east side of Africa. It's a big place and there is very little cross-continent connectivity that doesn't take the long way around via submarine fiber to Cape Town, and then up the east coast.