If you've already got a bike you love to ride, that fits you perfectly, then I vote for conversion. Otoh, if you don't have a bike you love, get a commercial e-bike. Conversions don't have to be ugly, there are fully wireless versions out there and your conversion will absolutely be a lot lighter weight than a commercial e-bike. By a substantial amount. So if weight matters to you (lifting and carrying up stairs, etc.) a conversion is the right choice as well. But if weight isn't an issue - no stairs, maybe a van to put the bike in instead of having to heft it on a rack, that advantage disappears.