Interpreting 50fps to 23.976fps in Premiere Pro
The recommendation from Adobe for slowing down motion is to use Optical Flow.  If you put a 50 fps onto a 23.976 fps timeline, select the clip and set Speed/Duration to 47.952% with optical flow, then you should get a good quality result.  And of course you are on your own for sound, because slowing things down 2x is not going to make any sense for the audio you recorded.

Shooting at 25 fps for a 23.976 timeline could be a 4.1% slowdown (in which case you might want to pitch shift your audio so you can keep it) or a re-interpretation (where you drop/optical flow frames) in which case you can keep your audio as is and mate it to the retimed video.

If you find yourself doing lots of 25->23.976 conversions, you may want to seriously rethink the idea of using a PAL camera do make NTSC deliverables and instead buy a camera that is NTSC-friendly.