Currently a FiiO M3K and I've been super happy with it. Might be discontinued now, however.

The thought process for the purchase was that I wanted a standalone DAP without a touchscreen (iPod-esque), without wireless connectivity, with expandable storage, and not running Android. The M3K also has good Rockbox support including dual-boot, so I swap between that and the native Linux firmware at times.

I am considering getting a second device of some kind with Bluetooth because there are occasional but persistent times where it honestly would be nice. Ideally it'd still be running a pretty basic OS, though.