There are so many different accents in English speaking countries that it is impossible to say what is best. It is also true that most people who speak English will have trouble identifying other English accents from outside thier country or region. If you go to Canada or the US, many (most) people cannot tell the difference between an English/Irish/Scottish/Welsh or even Australian accent, unless it is a thick, stereotypical one.
As for being substandard or hard to understand, there are accents like that everywhere. For example, I usually find most British accents easy to understand, but, just the other day, a British Teenager asked me for directions and he had the "mahbles in the mouth" British accent, and I had to ask him to repeat himself several times. I travelled to Dallas several years ago, and not everybody speaks like cowboys or race car drivers. Although I've never been there, I hear that not everyone in Australia speaks like the Crocodile Hunter either.
If you're going to College or University in an English speaking country, it's likely you will pick up a clear and understandible version of English. If you want to hear the differences between Canadian and American accents, watch a Candian news program and then an American one. You will hear subtle differences, but both are easy to understand.
As for being substandard or hard to understand, there are accents like that everywhere. For example, I usually find most British accents easy to understand, but, just the other day, a British Teenager asked me for directions and he had the "mahbles in the mouth" British accent, and I had to ask him to repeat himself several times. I travelled to Dallas several years ago, and not everybody speaks like cowboys or race car drivers. Although I've never been there, I hear that not everyone in Australia speaks like the Crocodile Hunter either.
If you're going to College or University in an English speaking country, it's likely you will pick up a clear and understandible version of English. If you want to hear the differences between Canadian and American accents, watch a Candian news program and then an American one. You will hear subtle differences, but both are easy to understand.