The biggest benefit is the ease of cleaning. Another thing to keep in mind is that single hungs are generally designed for low-priced, new construction use, so there are not many quality single hungs on the market based on little demand. This could be an indicator of window quality for you, its out of the ordinary for a window company to come in and recommend single hungs.

I‘d go double hung in all.

Yes, I like the idea of double hung for upstairs. Getting bids now. Expensive, but I'm so glad we're doing it bc the windows are old original single pane, totally not energy efficient and ugly.

No one uses single hung windows anymore. I question any company that would push that.

Do yourself a favor and go with double hungs.

Double hung