Hello Vic,
Very slight differences!
Some words and vocabulary are different in both ( as in yo and vos), but basically they are the same and you would perfectly understand someone speaking Argentinian Spanish, if you have only learned the Spanish spoken in Spain or used Spanish websites.
The same goes for British and American English.
Some different words used specially in informal speech, but in general you could make yourself very well understood speaking any of them with someone speaking the other English.