I asked whether you were playing Deuces Wild or JoB, and then ignored the answer apparently!

In JoB, the correct play, as several have pointed out, is to hold only the ace. But it's correct by a very slim margin. Here are Dancer's statistics:
RETURN HOLD
2.3826 ___A_
2.1277 _75_9
1.7539 __5A_
1.7081 _____

In Deuces Wild, the straight flush possibility is on top, but again not by much:
RETURN HOLD
1.7021 _75_9
1.7021 875_9
1.6081 _____

It's interesting that statistically, there's no difference between going for a straight and going for the straight flush: your expected return is the same either way. Counterintuitive indeed!

Michael