In order to be the best, you have to learn from the best. That has been Australia for the last 20 years, certainly (with a few minor hiccups).
In the sixties and seventies, the West Indies reigned supreme, although the South Africa side of the late 1960's seemed to have the greatest balance of any team I have ever seen.
Could England become the best? Doubtful, but that shouldn't stop them from trying.
Pakistan? They certainly seem to have a pretty reasonable conveyor belt of fast bowlers, and I have always thought that a team of great bowlers will have the edge over a team of great batsmen.
India? See my previous comment about bowlers and Pakistan.
South Africa seem to be in a rebuilding process at present. Shaun Pollock is a magnificent bowler, and any attack which has the likes of Ntini and Kallis in it cannot be discounted. They have also (today) appointed Graeme Pollock as batting coach to the UCBSA, which is one of the more sensible appointments I have heard of recently.
West Indies? No.
Sri Lanka? No.
New Zealand? About the same chance as England. Bowling has depth, but not 'strength in depth'.
In short, Pakistan might, South Africa could, the rest... hmmmmm.