Hi.
That is such an open ended, complicated question.
The first thing is, in any country there are good and bad areas for any species, the fact is, there are areas with good Leopard hunting in most countries where it is legal.
There are also some regoinal differences in body size for these cats:- really big toms can be found in Southern Zimbabwe, some parts of Zambia and Tanzania, whilst smaller bodied ones are found in the Zambezi Valley, Cape Province in South Africa and the remaining parts of Zambia and Tanzania (the same applies to Mozambique).
I don't believe there are too many people who have done enough hunting in most African countries in recent years to be able to conclusively answer this for you, as it is only possible to hunt so many concessions per season per country.
We all have our favourite areas, in countries that we hunt in a lot and know well and would be biased in our answers, if truth be told.
I wish you the best with this, but if you are thinking of a safari for Leopard and are after a really big tom then look at the trophy galleries of the prospective outfitters, you'll quickly tell whose areas have big cats. But please remember like any animal, Leopards habits and patterns change, sometimes inexplicably, and where there were 3 males on baits a week before you arrived, suddenly not a track can be found!! Obviously the reverse can also happen, that is the essence of hunting and wildlife in open areas, if we could gaurantee the outcome, it wouldn't be worth doing.
Some areas have good Leopard but they have been persecuted by cattle ranchers for years and are very wily, this is the best hunt to me, since when you finally work out that old boy's pattern(sometimes after a couple of seasons) and get him in front of the blind for a shot, that feeling when you know he has arrived and all the hours working him out have paid off, awesome!!!!!!
I hope this helps a bit.
All the best for 2010 and happy hunting!
Regards Rod