I'm using KeePassDX on Android (sync'd to KeepassXC on PC using syncthing). It works quite well and the GUI feels quite polished.

Of all the Keepass implementations in Android it seems to be the most actively maintained and featureful, but it's great to have a few different options. In addition to KeePassDroid (which I used to use, and have no major issues with) there's another (Authpass) on F-Droid which I haven't yet tried but looks promising.

The only issue with KeepassDX is that it doesn't yet support yubikey NFC for challenge response mode, although it's on their roadmap I believe.

No, hadn’t even heard of it (or forgotten about it), it didn’t exist when I chose K2A, and I’m not having any issues. Might check it out anyway.