I found this page:
http://mitchell.casinocitytimes.com/articles/12581.html via Google; too bad the information is from 2002.
Notice an interesting trend? It seems the higher denomination machines you play, the better the payouts. You won't even see 94+% until you play the $5+ machines. I wonder if that's still true today.
The best slots for that month seem to be at AC Hilton, which paid a whopping 101.3% for the $100 machines.
edit:
Check out the results from
this search, and it seems this trend is still in effect (As of 2006 at least)