Statistically, you are correct -- keep the straight and get $20 return for certain.

But the other way, you have 4 possible outcomes -- zero, $20 (another straight), $25 (a flush) or $250 for the straight flush.

I can afford to lose $20, which I may spend on lunch anyway, but $250 would buy a nice chip, even though there's only 1 card that hits it! I would probably take a shot at that level (and get a hot dog for lunch if outcome is zero ). On the other hand, if playing at 5x or 10x those levels, I would stand pat with the straight.

My total time playing the poker machines is probably only 10-20 hours per year. So my odds are short-term anyway. If I were playing 1000 hours, I'd follow the odds more religiously.

Just my thoughts.