It's always best to play max coin - if you cannot play at the desired denomination, you should then move to max coin at a lower denomination - for example change from $1 coin to $.50 or $.25 wagers.

Also watch your 'Top Line' award - it's been suggested that a one-line, three-reel, 3 coin machine with a 4000 coin 'Top Line' award will jackpot aprox. 3 times more often then the same machine with a 10,000 coin 'Top Line' award. (Provided they are Class III machines)