fps resampling dilema
48 to 25 should be better because you have more frame information to interpolate, though the contents of the clips could also matter.  If all the 48 fps clips are high speed motion while the 25 is relatively static shots, then it will probably interpolate better.

The key is that frames are going to have to be guessed at and the less time that passed from the last frame that can be used for the guess, the better off you will be.  Since 48 frames much closer to the correct timings it should generally get a better result.

Ultimately though, I'd suggest trying both interpolations and see which looks better to you.  While what I explained is a good general rule, sometimes the content of the clips makes weird things happen and there's no replacement for trying it out to see.