There are a few spelling differences between all three. British and Canadian add a "u" in many words like "colour" and "neighbour," and British uses an "s" in words like organise and recognise, whereas Canadian and American use a "z". Also, the word "orient" as in "disoriented" or "to be oriented" is actually "orientate," so instead of "disoriented" in Canadian or American, it's "disorientated" in British. The expressions and vocabulary used in American english differ greatly from ones in Canadian or British English, for example a "truck" is called a "lorry" in British. There are a tons of other differences in vocabulary and expressions. Hope this helps!

I think the main difference is the accent. There are slight spelling differences (Like Jenn mentioned) but nothing that will matter. Then there local words like "Garage" / "Shed", "Jandles" / "Sandles". Then there is slang (which changes all the time) like "G'day mate" or "Yeah man". In the end if you learn British English or American, New Zealand, Canadian it doesn't matter. You will be understood everywhere.

America, and the world... speak English because of England (period). We owe our violence to the Romans and our language to England.

American English is the one that sounds the best, of course! Like Jenn said, there are spelling differences, and may words and expressions have different meanings, just as some of the Spanish words and expressions you have in Columbia have different meanings. or are not used, in Spain, or even other Latin American countries. If you were in Spain, it would be better to learn more of the British English, since you would probably have more contact with the British than with Americans. Being in Columbia, you may want to find language partners from North America, preferably the United States, eh, Jenn! ;)