The other day I was talking with a lad from Hong Kong. We were speaking mainly in Mandarin, with odd bits of Cantonese thrown in from time to time – I speak Mandarin fluently, but only know a little Cantonese. I asked him how he had learned Mandarin, and he said that he had just picked it up through listening and speaking, and that it wasn’t too difficult. I’ve heard similar stories from other people from Hong Kong and Macau, and suspect that it is easier for Cantonese speakers to pick up Mandarin than it is for Mandarin speakers to pick up Cantonese or other varieties of Chinese. This is partly because Mandarin is phonetically and grammatically somewhat simpler than the other varieties, and also because there are far more Mandarin speakers, and media in Mandarin is far more common.
Have you experience of the relative difficult/ease of learning different varieties of Chinese?