I wouldn’t dare to correct my many Spanish-speaking friends and relations to their faces, but I’m fairly the dialect most commonly heard around here would be fairly difficult for someone from say, northern Spain. Then again, with the amount of borrowed English words using Spanish grammar, perhaps it’s more of the language being a creole than just the accent when things get that mixed up.
Of all the accents that I find hard to get used to is Caribbean accent (Cuban, Puerto Rican, and Dominican) and, ironically, some of regional Spain accents. Caribbean accent is just that they tend to speak way too fast and convert "r"s to "l"s. So. For example, “Yo quiero un nuevo carro.” To my mexican ears, they sound like “Yoquielounnuevocalo.” 
Argentinans are not as bad if you are into soccer. I guess I am used to streching the “LL” to its limits.
Depends. Certain regions of Venezuela and Puerto Rico share a Caribbean accent.
…and sometimes, I 'm not too good with English, either. Gads.
From my Mexican pov, it depends on who you are speaking with. Caribbean accents, once the speaker slows down, it’s no problem, at least in my experience. One of my cousins is married to a Dominicano. At first, for the life of me I could not understand a word he was saying. Too fast. "L"s where they shouldn’t be. But. After talking to him after a good amount time (and he slowing down), I can understand him w/o a problem.
Its probably due to a wider range of sounds in Portuguese that are not present in Spanish, all the nasal sounds.
I have a MUCH easier time understanding Mexicans and South Americans then I do Caribbean Spanish, its much slower and much more clear
Well. Argentinans are well known for making a strong “ll” sound than the rest of the Spanish speaking countries. For example, “caballo” (horse). Generally, it should sound like “ka-Bah-yo”, but in Argentina it spoken as “ka-Ba-Sho.”
Just guessing, but most Brazilians probably hear lots of Spanish whereas Spanish speakers aren’t exposed to Portuguese that much. The written languages are quite similar, but the pronunciation is very different. I can understand Spanish pretty well and find written Portuguese pretty easy to understand, but I can hardly understand any spoken Portuguese. I get more from listening to Italian than I do from Portuguese.
I agree that, as a non-native speaker, Cuban Spanish is the hardest to understand. All the words sound like they’ve been run together and have had the last syllables lopped off. Does Cuban Spanish even have an “s”? 
Maybe you weren’t so clear in the OP, because I thought the same thing as **Wendell **when I read it. Does she really have difficulty understanding British actors? There are some British regional accents that are pretty thick, but do you have problems with, say, a James Bond movie? That’s kind of hard to imagine…
No, I don’t have problems with a James Bond movie. Like I already said, I do fine with most programs. The last movie I can remember having any trouble with was “The Full Monty,” while the people I was with really struggled. Since I don’t do much hanging out on baseball diamonds with the British, I gave an example in the OP of a time when I’ve encountered accents I couldn’t decipher.
Now, I assume someone will come along and say how impossible that is.
OK. But in your OP you said it was a “struggle”. I think that’s where the confusion came from.
Venezuelan living in Puerto Rico, here.
In conversation, there is no way you cannot understand someone else from another country. There might be some word choice issues but nothing critical. As long as both parties are making an honest effort to understand and be understood, pronountiation is very similar from country to country.
Ditto for newscasts. With a more standard spanish and trained diction, they are very easy to understand no matter what country they are from.
Watching movies from Spain normally requires my full attention. Sometimes it can get really hard, as they speed and use all kinds of slang.
When it comes to slang, though… It seems like all countries have made a deliberate effort to choose their sexual euphemisms from the daily food items of their neighbouring countries. Put a handfull of assorted latinos in a room and in less than 10 minutes, the topic of conversation would be “what does x mean in your country?”
And no “R’s”. 
I can almost hear my Boricua friends.
And part of that creation of a “standard Spanish” is the radio and television media. The tevenovela industry has also helped create a “mainstream Spanish” that is easy on the ears. Columbian, Venezuelan, and Mexican tevenovelas are always popular in the Latino communities in the US.
LOL…Dot’s use “papaya” in Cuba. We don’t mind in Mexico.
Jesus Christ. I said “I can struggle.” If you never have, bully for you. Really. That’s peachy keen.
Now that my story has been vetted by the Doper truth squad, can we get back to talking about Spanish speakers?
Ah, don’t take the bait. Some people are just buttmunches no matter where they are. I have trouble with a couple of English accents, particularly if they’re spoken quickly. Seeing as how I’m from The South, I like it when people talk all slow like and use small words my piddlin’ lil’ brain can reckin.
Hey, pardon me for simply trying to explain why someone didn’t understand your point. If you don’t see a difference between “I can struggle” and “I do fairly well”, then I don’t know what else to say.
In this case context probably makes it easier. The pitcher and catcher already have some idea what they’re going to be talking about (pitch selection, throwing mechanics, holding the runner on, etc.), and a lot can be said with a limited, special vocabulary.
FWIW, I have trouble with some of the lowbrow English accents, at least until I get used to them. I couldn’t get into the English version of “The Office” because I bored to easily of trying to understand what those wankers were talking about. “The Full Monty,” on the other hand, I had no problems with after the first couple of minutes of getting accustomed.
In Mexico I hear ChicanoRojo’s Argentina-style “ll” used from time to time. I don’t know if it’s people being presumptious or what. In fact the earliest occurance I recall was one of my Spanish teachers in Mexico. “Zho fui a montar caba-zhos azher.” Her whole way of speaking was outside of the norm that I knew for that region at that time, and I had to ask if she was from Spain or some other weird place. Nope – just from the state of Veracruz.
Also in parts of Mexico I’ve heard something similar to the Carribean accent. Also anyone from Sinaloa was incomprehensible, and it took me a few weeks to fully understand people from Sonora. People from the central – Guanajuato, Michoacan, and Jalisco – are the most intelligible to me, but then again, that’s what I’m used to.
My father-in-law semi-regularly clips “-ado” to Carribbean style “ao,” but he knows it’s wrong for the region and does it just for fun. Funny thing is, I catch myself doing it now when I’m being funny (or even less-than-funny).
Oh, crap, just for the sake of completeness, you know how we make fake Spanish by adding -o to words? Mexicans make fake English by adding “-ation” to words.