Since I proposed first I bought the engagement rings and she bought the wedding bands while on a trip to Mexico. We do have a joint account though and would have paid from there if she hadn't already decided to get the bands during her trip.
We paid for our bands out of our joint account. So technically, we are both paying for both bands. If we did not have a shared account, we would each pay for the other persons.
I bought his, he bought mine. It was totally unfair as his was very cheap despite my objections. Mines a bit flashy but we saved big getting it pre owned. I kind of like that we gifted them to each other.
I paid for my husband’s band. We were going to skip a wedding band for me (my e ring is weirdly shaped) but my MIL and my, now, late GMIL had a custom ring made by my husband’s uncle (is an UIL a thing? )
Since ours are pretty much the same-ish price, we decided to combine the cost and just split it 50/50 to keep it fair. He offered to buy mine and I'd buy his, but that felt unfair to me.