I oversized mine slightly and don’t regret it. The biggest benefit was faster heat up times. If you’re only heating occasionally, it’s nice not waiting all day to gain a few degrees.
I went way oversized and probably wouldn’t do it again. It heats fast, sure but the upfront cost was high and I don’t really use that extra capacity most of the time. If I were doing it again, I’d stick closer to the sizing charts.
Climate matters a lot. I’m in a cooler area so the larger heater helps offset heat loss on windy days. For warmer regions, I don’t think oversizing gives as much benefit unless you’re impatient like me.
From what Joe Smith mentioned about upfront cost versus real usage, I lean that way too. I went slightly bigger than recommended thinking faster heat-up would be worth it, but I mostly heat on weekends. Yes, it warms up quicker, but I also noticed the fuel cost when pushing it hard. For a medium pool used occasionally, sticking close to the sizing charts is usually enough, especially if you use a cover to reduce heat loss.