They lead the league table devised by the game's authoritative Wisden Cricketers' Almanac and are narrowly ahead of joint second-placed Australia and West Indies.
The South Africans owe their ascendancy to Australia's defeat last week by India.
``But the top five teams are so close that any of them could be champions by next April,'' said Wisden's editor Matthew Engel.
England are seventh, ahead of only Zimbabwe and New Zealand, and behind one-day champions Sri Lanka.
The table awards two points for winning a series, one for drawing and none for losing, taking into account fixtures since October 1990. The difference between the number of series played and points gained determines a country's placing.
Standings 1. South Africa 2. Australia 2. West Indies 4. India 4. Pakistan 6. Sri Lanka 7. England 8. Zimbabwe 9. New Zealand