Well despite all the variables, you still need to pick one....so which one? I mean if I handed you $500 and said "Okay you can only play one slot machine and you have to put it all on that machine....pick one". Don't think too hard about it!
Ok, so I would probably play a reel-power/any-ways type game. If I was lucky enough to hit something, I know it would be rewarding.
There are many slots which have increasing jps which MUST HIT by a fixed dollar amount (on some $1 that must hit number could be as much as $5,000). [The increment is sometimes based on play and sometimes WINNING play.]
I would gamble my bankroll on a machine that (1)increments with play, (2)near the "striking value"--such machines may be hard to find, but they DO exist.
[At Bellagio (in LAS), about a year ago, there was a PENNY slot whose striking value was $10,000 and was in the upper $9,000 range, I played abouit an hour and ran out of money, so the next player might have won $10,000--a month later, that machine was no longer on the casino floor.
A VGT three reel. $1, $2, or $5 machine. Those are pretty much the only machines that I feel good about doubling my money on nowadays. If you get on a hot one you can take just $20 up to $1,000 and beyond in no time.