Hola Travelbug (and others who may have the same questions),
I'll leave your other questions alone because there is plenty written on them and for the most part it's even more subjective than the answer to your first question.
Disclaimer: I learned Spanish from absolute zero in Buenos Aires and have never learned Spanish in another country.
With qualification in place, I worked in the language learning industry for a while and that "Buenos Aires is a poor place to learn Spanish" is one of the most oft repeated myths about the Spanish language that I hear from foreigners. Right up there with "argentinos don't use the preterito perfecto" and "'b' and 'v' are perfect homophones in Spanish."
First of all there are many of different accents in Spanish, which not only vary by country but usually by reigion as well. The Spanish spoken by most Mexican Americans sounds nothing like the accent you hear in Mexico City. The Spanish on TV here sounds nothing like the Spanish spoken in cordoba for example. If there is no universal Spanish accent then why is the Argentine accent inferior to others as an environment for learning Spanish?
Those who perpetuate the myth about learning Spanish in Argentina usually cite one of the following:
"The argentine accent is difficult to understand for most Spanish speakers"
First of all, after several months of Spanish clases here you will not have an Argentine accent. I've lived in Argentina for 5 years and speak Spanish at least 30 minutes for every minute I speak English and consider it a success that people finally don't inmediately identify my accent as an being from the US. Most commonly people guess that I'm from Spain or occasionally Russia (no idea why). Even Dustin, the internationally famous YouTube star whose videos highlight him as the Yankee who speaks Argentino, and who is clearly a natural when it comes to imitating accents, has a few tells which give him away as a non native speaker.
Secondly my purely anecdotal experience with Buenos Aires Spanish is one of being understood. Since learning Spanish here I've traveled to 5 Spanish speaking country's and conversed in Spanish in the US and have never had any real difficulty communicating. There is a fair amount of Argentine media distributed overseas and most Spanish speakers are accustomed to the accent although probably not completely familiar with regional vocabulary. Sort of like if an American is talking to an Aussie, it's a wired accent sure, but it's still the same language and it's not that hard to understand.
Finally this idea of Argentines having difficult to understand accents - accents not vocabulary - seems to be one that is unique to native English speaking foreigners in Argentina. If you were to ask native Spanish speakers who've traveled extensively most would probably not consider the argentine accent difficult to understand. They'd usually say thinks like the Chilean accent, the Andean accents, the 'rural Mexican' accent, or even the Cuban accent (which I think is pretty clear).
"In Argentine Spanish they use the voseo and if you learn that you wont be able to talk to anyone else"
This is a non issue really. Learning the voseo conjugation takes about a second and doesn't mean you can't learn to conjugate in the tu form. Here I'll teach you the voseo right now: Take the infinitive of any verb (other ser, ir or haber) and add an accent to the second to last letter and change the last letter from an r to an s. For the imperative just drop the S. There now that youve mastered the vos form you can concentrate on the Tu.
Not to mention if you forget and end up using the vos form outside of Argentina, everybody will still understand you!
"They have different words for everything"
Again this is true in every country. Just like different English speaking countries have different words for the same things. It's rarely impedes comprehension.
"The shhhh sound is odd and nobody will understand you"
The sound of ll and the y vary quite a bit from one country to another and run the gamut from the "sha" here to "yah" "cha" and even "jah" in other parts of Latin America. Nobody is going to confuse your yeismo with another phoneme.
Basically, don't worry about it, Argentine spanish isn't harder to learn and it's not any less useful. It is still castellano after all.
