What kind of slot machine is the best to play?
Simple answer with no math: If you want to play while not losing too much money then play penny games at max coin, min bet per coin. (Bet $.20 or $.25 per spin for example.)
If you want to bet a lot and don’t mind losing then you should play quarter or dollar machines.
Here is the math behind it:

This means that if you play pennies and cover all lines on a 25 line game it will over time only cost you $16.50 per hour to play.
Compare that to a $3 bet on a dollar slot for a whopping $108 dollars an hour on a dollar machine and you see why pennies are so good.
BEWARE: IF YOU BET PENNY MAX LINE AND MAX COINS ON A PENNY GAME YOU WILL LOSE YOUR SHIRT!

Note: This is a simplied math model. The payback assumptions are general industry ranges and don’t illustrate what any individual machine will do. Also this would just be an average. The payout percentage is over time, not for each time that you gamble.