I was a die-hard Opera user when it ran Presto - I tried the Chrome version for a while, & I have Vivaldi installed so I can periodically open it & try it out for a while, but absolutely everything since Opera 12, Vivaldi included, has paled in comparison.

Opera 12 was instantaneous in everything it did, even with a session with 100s of tabs open (without auto-unloading them in the background like modern browsers do) & thousands of local emails in M2. The instant history navigation in particular is something no modern browser has even attempted to copy, Vivaldi included (likely because it's a core Chromium functionality that would be difficult to override).

There's just so many tiny details of its UX that were slick & seamless & have been lost. Little things that seem minor but were huge on aggregate like text selection of linkified text - it simply does not work in Gecko or Blink browsers but somehow Presto did it with ease. The page you're leaving remaining fully responsive during navigation to facilitate change-of-mind on mis-clicks, etc. Millions of tiny UX details like this just made the whole daily browsing experience so painless.