Overnight train often do have fixed schedule & less chance of make-over (as seldom they gets late), while long distance train always have the crippling chance of getting late, on the way & hence the make-up always goes on.
But here, both train depart right time from NDLS & till ALD, both are overnight train, with less slack, as with more stoppage, Prayagraj dont take much time than Purushottam!! If have to travel in SL, then definitely Prayagraj is a toss, but CBC rake is severely in pitiful situation, AFA washroom is concerned!!