To answer the question, I love the differences between all of them, however:
Italians tend to talk very freaking fast. So fast, in fact, I had to stop watching a fascinating Italian detective drama because I knew the subtitles were not keeping up with what they were saying, and I was losing details.
Some Eastern European accents are very harsh.
Like @janbb, I really enjoy the “celtic” accents – Welsh, the many forms of Irish, and Scottish.
Cornwall and Yorkshire, England (two ends of the country, two very different accents). I don’t care for Birmingham as much… too many “f“s.
Portugal. OMG. Swoon.