Vivaldi just had a nice update with an auto-hide feature.

I am a fan of vertical tabs but usually it takes up a little too much left hand space for my liking so I'd semi-frequently be adjusting the size depending on if I needed it, now with the recent change all of it gets out if your way until you hover over there, I'm liking it a lot so far.

Both Chrome and Firefox's vertical tabs are so much worse, Edge's somehow the best out of the mainstream browsers imo.