The absolute best! I have been using Opera for about 16 years or more and have always found out that it has no competition, not even close!
The best level of customisation, tab management, browsing speed, add blocking and, what is most important, the least resources needed from my laptop! I frequently use between 250 to even 500 tabs open at the same time, so this is a major point for me! In comparison, the other browsers slowed down, froze or used most of my RAM when browsing with even as little as 50 tabs opened.
So congrats for building and maintaining the best browser on planet Earth!