Side by side most of the time. I put them on arms so I can move them around and swivel them. It's ridiculous having two 34" Ultrawides. But, I can. So I Do. I also run a 3rd 40" 4k display when I need it or want to sit further back.
Yeah I went from 1 32" 1440p and two 1080p side monitors to just a single 4k 43" and I'm saying that the time of multi monitor setups has come to an end.
I just made the switch from 3 24 inch monitor to a single 49 inch super ultrawide. It's basically 3 monitors with no bezels. A lot of things are annoying though like full-screening videos/games but there are workarounds.