The old rule of thumb is that higher denominations had a higher payout percentage. On many games the payout distribution increases moderately for the lower pays but the top awards pretty much remain the same. Small pays keep me interested longer. Ie 3 coins in 2 out.

Many casinos used to put their loosest machines by the doors - the intent was to attract more customers. Of course the volume was always cranked on them too so most people would move more indoors away from the traffic and noise.

Machines with progressives typically have lower payback percentages as a certain % of each coin is added to the progressive amount.. Over all the presence of a progressive doesn't impact how the machine does or does not pay out.

In a couple of these sentances I used the words "used to"...
The new slots which are often designated as penny machines often take multiple coins per line and have multi-lines. Ie 20 coins on 50 lines at even a penny is now $10.00 per spin. Ouch. If it wasn't for the many small pays that you hit a $50 would last you 5 spins and all of 3 min.

I personally like the old 3 reel (not 5 reel) 3 or 5 coin multi-line slots. Ie 5 line Double Diamond Deluxe with a $1.00 denomination and a progressive.