Excellent Post!This is an interesting one, insofar as how wide a scope are we looking at - a country's top couple of performers? Top five, ten, twenty? Or the average quality of everyone they've ever produced? I think my answer would differ depending on how I looked at it.
A lot of people are voting for Australia as the leading producer of batsmen but I'm not sure I'd agree with that. Bradman of course tilts the balance hugely, but I'd argue that if you removed him from the reckoning and looked at, say, the top dozen or so bats from each country then both England and West Indies are better than Australia man-for-man. Of course if you take a longer-term look then the depth of talent available to Australia over the course of cricket history means that their list of quality batsman is longer than that of the West Indies, and probably much-of-a-muchness with England. For opening batsmen, it's clearly England. For middle-order players, I'm torn between Australia and the West Indies. Overall, it's inconclusive in any direction.
It's a similar story with fast bowlers. Most people are choosing the West Indies as the clear number one, but I'd argue that the pool of great fast bowlers produced by Australia can match up to that of the men from the Caribbean. However, Australia's great fast men are drawn from a period covering virtually the entire history of Test cricket, whereas most the West Indian greats came from two overlapping generations, and thus man of them played together in the same teams. That so many champion quicks appeared for one country so close together possibly clouds our judgement in their favour. Again, I don't know which way I'd lean, a dilemma further exacerbated by the fact that England come well into the reckoning too, particularly if we include their great medium-pace and fast-medium bowlers (Lohmann, Barnes, Tate, Bedser) in the mix. Pakistan and South Africa might also have a fair bit to say about this.
As for all-rounders, they bring their own questions. While the West Indies produced the single greatest of all, his supporting cast is pretty small. New Zealand have produced a collection of very fine players, while Pakistan have a couple who rank with the very, very best. However in my opinion it comes down to three - Australia, England and South Africa. Today, I think I'd argue that that the pool of genuine world class all round talent South Africa have given us - Faulkner, Goddard, Barlow, Procter, Rice, McMillan, Pollock, Kallis - probably puts them at the top of the tree. Then again, ask me tomorrow and I might say England. Or Australia.
I think wicketkeeping / wicketkeeper-batsman talent is a clear Ashes battle between England (Strudwick, Ames, Evans, Knott, Taylor, Russell, Stewart, Prior) and Australia (Blackham, Oldfield, Tallon, Grout, Marsh, Healy, Gilchrist). Other countries have produced individuals who can sit comfortably in this class, but none have produced anywhere near so many.
One area where I'm more than happy to pick a winner is spin bowling, which I'd give unquestionably to Australia. The only other area with one country so dominant in my opinion is England with its opening batsmen. After Australia, I think India or England probably come in next. Sri Lanka's pre-Test history saw some fine spinners who never had the chance to play at the highest level, and of course since then they have given us possibly the very greatest of all.
Finally, fielding - which is a hard one to measure. Australia and England have both obviously produced great fieldsmen over the course of their history with a 130-year pool of players to choose from, though of course a great fielder from the 1890s looked a lot different to a great one from the 1990s. The West Indians have had some wonderful fielding talent and the champion sides of the 1970s and 1980s set new standards of fitness and athleticism, while during the modern era South Africa and Sri Lanka have arguably led the way. So, take your pick of any of them really.
Something that stands out is that England and Australia rank at or near the top in virtually every category - though this is hardly surprising given that these two countries have played the most Test cricket and produced the most Test cricketers over the longest period of time. It will be interesting to see how - if at all - these lists change after another generation or two.