I loved Vivaldi's configurability. But it's sync is slightly moody as well. It can fail for a while. Though it is better than Firefox's in that it fixes itself.
But Vivaldi doesn't support bookmarklets and I use those a lot.
They have completely redone their sync implementation a couple of months ago, which seems to have fixed all the lingering issues (and also added E2EE, which I consider the bare minimum in any case).