What's the difference between all these accents...?

Well I can tell you the Boston one b/c that's where I'm from. Bostonions don't pronounce their R's so 'car' would be pronounced 'cah' and 'flower' would be pronounced 'flowah.' That's why people love to hear Bostonions say 'I pahked the cah in Hahvahd Yahd." :)