Well most Europeans I have talked to said American English would be easier to understand - but I guess English is English and as long as yours is good enough.... ;)

If your English is good enough, it doesn't matter. However, most people in Europe learn British English.

I believe a British accent would be easier. We have whats called a 'Received pronunciation' accent. This is very neutral, and is used on the news (and by the queen!) as it is the easiest to understand. However, there are so many accents in both America and Britain, so comparing between them isn't so easy!

A European accent is best.

In my own point of view,I think American English is easier for me to understand.But I don't think american english is a kind of standard language,british one is more standard,so I prefer learning british english,but I think american english is easier to speak