In the USA the three most common meat goat breeds are the Boer, Kiko and Spanish goats. Of the three the Boer breed is the most prestigious. You won't find Kiko or Spanish goat shows, but there are Boer shows in all parts of the country.
First bred by Dutch farmers in South Africa, the Boer goat was developed as a "meat machine" with fast growth and high birth rates. Kidding rates of 200% or more are common, and since they breed year-round it is possible for Boer to kid (give birth) three times in two years. Boer are quite distinctive in appearance, with short legs, chunky bodies and a white coat with a red head.
Since Boer goats are the most popular and best-known meat breed in the USA, breeding focus has shifted away from production and towards producing a "show-quality" goat. Pure-bred Boer goats are also quite expensive, with a proven buck or doe selling for $500 and up.
Kiko goats, on the other hand, are fairly rare in the USA. Kikos were bred in New Zealand for meat production, with a strong emphasis on ease of care - meaning goats who stay healthy, kid easily, and (in the case of does) are good mothers to their kids. Kikos were introduced to the USA around the same time as Boer goats, but breeders' focus has stayed mainly on production criteria such as parasite resistance.
Kikos are similar in build to Boers, although they are generally less chunky. Most Kikos are white but there is no color requirement.
Spanish goats have a very different breed history from the Kikos and Boers. Like the American Mustang horses, they are the descendents of conquistador livestock that escaped or were released by their owners. These wild goats ranged over parts of Oklahoma and Texas for 400 years before breeders took an interest.
Natural selection turned the Spanish breed into a relatively small, agile goat with a small well-attached udder. Their high level of adapatation to hot, brushy areas has made them a natural choice for meat goat producers in the American Southwest.
Because Spanish goats vary greatly in size, body type and coat color, it can be difficult to confirm that a particular goat is in fact a member of the breed. In some areas of the USA, particularly in the Southwest, Spanish has become synonymous for any "scrub" or "brush" goat.
To summarize, the Boer goat will probably out-produce the other two breeds over time, but is more expensive to purchase and is more likely to have health issues. The Spanish goat is exceptionally hardy but hasn't been "bred-up" for production, so it will produce less meat per head. And the Kiko goat falls somewhere in between the other two breeds, with better meat production than the Spanish goat and fewer health issues on average than the Boer.
So which breed is the best fit for you? It depends on your circumstances. Do you want to participate in goat shows and/or 4-H? Then your best bet is the Boer goat, since the other two breeds rarely have shows. Do you live in the Southwest and want a "low-maintenance" goat operation? Stick with the Spanish breed, which has proven survivability in the Southwestern rangelands.
Want a goat that has been selected for production AND survivability? The Kiko goat will probably be the best fit for you.