due dilligence... almost all = large majority. I didn't walk around with a clipboard and spreadsheet of manufacturers and ask players what machines they liked. You can learn a lot from observing.
As for which casinos, the ones in my local market (St. Louis area) and to the ones I've been to when traveling...Vegas strip and Tahoe most frequent stops.
Not sure if you even seen how it works, but when a player cashes out a ticket, the screen boldly displays the manufacturer. Look close enough on the screens and you'll see the logo of the manufacturer as well.
Sounds like IGT is working on design, that's great because people want to play winning machines but they also like graphically appealling machines.
Besides, I bailed at 15 for a quick 50% gain, so it worked out fine for me just riding a wave.