Argentina, should be mentioned here as well me thinks.
Not because they are better, but because they have become
HUGE as far as volume goes in the sport there is a huge
percentage of fight cards that include Argentinians (sp.?)

Baldomir, Mattysse et. al.

Look at the fight listings for tomorrow, 7 seperate events in Argentina
And another on Saturday

As far as the topic at hand goes.

I have to go with Mexico for now, I am not validating the per capita argument
And all things considered Puerto Rico is an American Territory.

So for me the order is this

1) Mexico
2) Puerto Rico
3) Cuba
4) Columbia
5) Argentina
6) Panama
7) Nicaragua
Brazil