You should try and find a machine with a paytable that pays at least 9 to 1 for a full house (45 with 5 coins) and 6 to 1 for a flush (30 with 5 coins). This is considered a 9:6 machine and would have a payout of roughly 99.5%.
If you can find a better paytable by all means play that game 9:7 machines pay 100.7% so that puts the odds in your favor assuming you are using an optimal strategy.