78 can make more straights than 79, so the chance of flopping a straight is the same.


456 (78)
569 (78)
69T (78)
9tJ (78)


78 can make 5 (2 card) straights.



568 (79)
68T (79)
8TJ (79)

79 can make 3 (2 card) straights).

Obviously the hand with the most chances of making a straight should make the straight most often.