I've settled on Topo Maps US (by David Crawshay) for now. Pros: 100% free, no ads or membership, easy to use, super nifty freehand distance measuring tool.

Cons: Map tile downloads take a long, long time. If your device sleeps during a download you may have to restart the download.

I want to run this app on both my iPad and my iPhone. It has a little WebDAV server that you can turn on to download map data. You can then upload the map data to your other device (no direct connectivity between iPad and iPhone that I could make work). This saved me hours of download time, but it's probably too fiddly for many folks.

Make no mistake: there are a lot of good reasons that Gaia GPS is so highly rated. But this app works for my purposes.