Choosing a Spanish keyboard layout for Windows?

Hi guys! So I want to add a keyboard layout for Windows 7 but I’m bewildered by the number of different keyboard layouts.

1. Are the “Latin American” keyboard layouts for all the different regions (ex. Argentina, Bolivia, Chile, etc) all the same? As far as I can tell, they are, but then why are they organized like this? What’s the difference than between choosing Spanish (Argentina) and Spanish (Bolivia)?

2. What are the advantages and disadvantages of
a. the Latin American layout
b. The Spanish layout
c. The Spanish Variation layout

3. Which of these layouts are most popular? Does this vary by country/region? What do computers come with by default in Latin America? Spain?

A lot of little questions; thanks for reading all of them!