I'm going for India, but if the question was who develops it better then Australia >>>>>>>>>>>> everybody else. I don't know how many countries have a system better then the AIS System, if there is.. Sure the East Germans in the 80's, but a lot of their athletes were doped to the gills, and I don't know if Russia or China is a tad shady.
You obviously have Pakistan, but for some reason they can never pull their heads in for the greater good of their team, I'm not sure about Sri Lanka, but they have achieved a lot when you think how tiny the island is but with so many people, and Bangladesh, but it takes time to raise above their current levels. From what I've gathered there is some naturally talented cricketers there.
I've always thought about the West Indies, but the lack of money, cohesion (at a board level) and infrusture with always hinder them in getting the best of their players. TBF I don't always follow WI cricket, but when I see some of their players in the team, it looks a name was drawn out of hat for no apparent reason and thrusted in the role, despite not being good enough or currently not good enough. I don't know enough about England, out of interest, how many people like cricket compared to those who like football, especially as kids who rather want to play for one of the biggest clubs in the EPL and earn more then the GPD of a improvished African nation in one season. And how many who do make it are either substandard or are just injury crocks? The Academy was really something that should of been brought in years before it did, it might have stopped us from being robbed of Darren Gough or Craig White's (don't laugh, I rated him quite a bit as a bowler) career? Far too many journeymen cricketers who cruise by on the easy life as well.
South Africa do produce some really talented crickets, but then do have a lack of quality depth (If Amla does better then average 30 against Australia next summer, pick my avatar, and if it is Michael Jackson, your dead to me ), how many good openers or middle order batsmen or spin or fast bowlers who there who could replace any of the current lot and do well? Geniune question as well. Zimbabwe in my eyes are not a Test olaying nation, but I'll chuck 'em in the poll since officially they are.
New Zealand have been done before, and frankally a post this long has burned me out