What do best blocks mean?

In Filecoin Explorer , there is a Best Block menu item. My understanding is that the best block means one of block(s) in the highest valid tipset. Anyone can confirm this?

If it is true, it comes another question: which one is the best if there are multiple blocks in a tipset? is the heaviest one chosen? or the one with smallest ticket? I would think it’s the latter, but again, I appreciate if anyone can confirm.