For video, 2.7K (Cine for 24fps, regular for 30fps) in Wide mode on the GoPro Black 3+. You get extra pixels to stabilize, remove distortion and reframe with, and still get a 1080p output file. At this resolution, I haven't had any issues with props dipping into the frame either, unless I'm looking dead ahead and pitched far forward for speed or wind compensation.
You can set the GoPro to take stills on an interval while it's recording video, but that interrupts the FPV signal, so I avoid it. If I need stills, I'll pull them from the video, but it is admittedly a much lower quality than dedicated stills, even at 2.7K resolution. If you don't have an FPV setup, then that's obviously not an issue, but it's much harder to frame the shots.