I know the global rounds tend to have good problems, but other than those, which rounds tend to have higher quality problems? Sponsored rounds (which ones)? rounds with tons of authors? Are there any specific authors who always have incredible rounds? anyone have specific round recommendations?
Educational Round 1 to ~20.
VK Cup rounds, Technocup finals, Tinkoff Challenge, MemSQL Start[c]UP 3.0
Usually I look at number of upvotes on the announcement, if it's > 500, round promises to be good
For normal Codeforces Rounds, I think #260 & #278 & #302 are good. For Educational Rounds, I think Round 1~15 are prepared well. For Global Rounds, I think all four rounds have high qualities.
None of the rounds.