I love Vivaldi due to vertical tab bar
But I use Palemoon (Firefox fork with XUL) with Tab Kit for vertical tabs too
I think Vivaldi (based on Chromium) is great for one time browsing (open -> close)
But I got a bunch of sites I visit daily so I got them opened in Palemoon and open them when I need
With another extension you can also unload tabs (manaual or auto, config it as you like) in Palemoon like Vivaldi (called hibernate in V)