Is it better to meditate after exercise or after showering?

When your body is calm after a mild shower, you can switch into meditation with more ease.

You can also switch with relative ease after light exercise.

After heavy exercise, first slowing the body down meditatively and then switching into sitting meditation would be more wise.

There may be cases where you are practicing the mastery of your energies and can rapidly move into stillness after lively activity. You must choose consciously and track your energies consciously and act accordingly for the best results.