One beneficial variation is for the casino to raise the payoff for the royal flush from 4000 to 4700 coins. (Why such an odd number, you ask? That makes the jackpot just below the threshold for which the casino would have to file a W2G on you with the IRS. Neither you nor the casino wants that.) This raises the expected return of the game to a very nice 99.9%.
By the way, it is relatively easy to get a quick estimate of what a pay table variation will do to the net return of a game. Start with the payout table given above. Working out the 4700 royal flush example, you can notice that royal flushes account for 1.98% of the total return when the payout is 4000. Thus, when the payout is 4700, they should roughly contribute (4700/4000 * 1.98%) or 2.33%. (“Roughly” because in this case you can adjust your playing strategy slightly to pick up 1/100th(!) of a percent.) Thus this machine should pay at least 0.35% more than the standard machine–and it does.
On the other hand, the common “greedy Asian2Bet casino” jacks-or-better variation is to change the payout of a full house to 40 and a flush to 25. These machines are called “5/8” machines as opposed to “6/9” machines; the names come from the flush/full house payoff for a single coin. 5/8 machines give 2% or more back to the casino and should be avoided.
Some 5/8 machines will offer a progressive jackpot on the royal flush, one that starts at 4000 but then increases slowly until some player hits it. While it is true that if the jackpot gets high enough it can offset the disadvantage of a 5/8 payoff, I avoid progressive machines as a matter of personal taste. Saying that a progressive is occasionally in your favor is like saying that the state lottery is occasionally in your favor; it is true, but it requires you to actually hit the big payoff to realize the advantage. Also, my strategy was calculated for the 6/9 payoff, so your return will be off by a fraction of a percent from the optimal return if you use it on these games.
A relatively new gimmick used on 5/8 machines to make them more attractive is “bonus poker”–offering higher payoffs for certain fours-of-a-kind. It seems to be working; these machines are popular. Avoid them. The “bonus” only slightly compensates for the big disadvantage of the 5/8. On the other hand, “double bonus” poker is a good machine; its return is 100.17%, if you can find the full payoff version. There is a discussion of Double Bonus below.
A rare variation of jacks-or-better is tens-or-better. These machines pay on a pair of tens as well. These are actually “5/6” machines, as the payoff for a flush is 25 and for a full house is 30. Nonetheless, he average return for optimal play is almost exactly the same as the jacks-or-better machines. Yet it seems casinos steer away from them, and the few that offer them are exceedingly proud of it. I suspect that the problem with tens-or-better, from the casinos’ point of view, is that it is less susceptible to bad play than other machines. Even people who have no idea what they are doing can apparently get a reasonable return on these machines. Anyway, from your point of view as an expert player, tens-or-better is neither better nor worse than jacks-or-better and can be played when you are looking for a change of pace. I have made up a expert strategy sheet for tens-or-better.
However, tens-or-better has a lower variance than jacks-or-better. Variance is a mathematical quantity with an important practical consequence. A high variance game will be much more “streaky” than a low variance game. You will find yourself alternately plummeting, then being treated to a flurry of wins that put you back up ahead (we hope). This streakiness is a quality of a gambling game that some people like and others do not. If you like playing a high variance game, bring more money. For example, if I am playing jacks-or-better, I figure that $100 stake should last for as long a session as I am comfortable playing (which for me is three hours), even if I am relatively unlucky. If I am playing jokers wild (the highest variance), $200 seems to be the equivalent stake. And this is true even though the return on jokers wild is better than jacks-or-better.
Sometimes you will find machines that pay only 5 for two pair instead of the normal 10. This is a complete rip-off, and should be avoided at all costs. Two pair account for 25% of your total return, and cutting that in half gives an enormous 12% extra to the house, an amount that cannot be compensated for by increases to the payoffs of the rarer hands.