The challenge is, to have at least a quarter to a third of the African continent with a stable, prosperous, first/second-world country or set of countries with: paved roads, electricity, sewage, A/C, modern sanitary health care, relatively modern cars, safe drinking water across the country, people with a per capita income enough to let them purchase cars, TVs, video games and the like, at any point after 1800, using the colonial powers (UK, France, Spain, Germany). People from those countries would be able to afford to take vacations and fly to Europe or America. The environment would be safe/clean and have a moderate environmental policy to prevent pollution and exhausting resources. This should preferrably come with as little change to other countries' development as possible.
Which countries have the best chance for this, and which kind of timeline would you see leading to this?