Depends on the individual, but one of my breeder racks the group all goes in the far back warm corner. One of my babies chooses to poo on top of his hide. Some like the water dish, they all have their favorite sides. But for the majority of mine, far back warm corner. Silly little guys...
Most of my geckos poop in the warm side hide (which is in the back left corner of my tubs). I guess they like a bit of privacy. I do feel like males tend to be messier, because half of them just poop wherever.
Most of mine go on the warm side back corner. I do have a few that like to go inside the hide container no matter where it is and one enigma male who will only go I a small tea light candle holder.
Mine chose to poop in her cool hide. I figured Its better to move the hide and see if she'll stick to that one spot or follow the hide and keep pooping in it. If I can see it, means I can disturb her less but knowing my luck she'll just keep pooping in the hide.
I have reptile carpet in my tank, and a slate tile pile at the front but one long single piece at the back that both of my leo's poo, in their own separate spots in the warm back corner of the tank. I'm scared that they like the slate to poo that if I cover the whole tank in slate that they might not go there anymore, unless I keep that piece in there too so they still poo on that piece since that is the main thing I clean. I switch out my carpet every 3-4 weeks or so.
Lestat goes on the cool side (mid to front corner). Kovu and Daenerys do their business on the warm side, front corner. My boyfriend has two, Zombie and Rhaegal. Zombie goes in his warm hide now, but he used to always go on the cool side, back corner. And Rhaegal goes on the cool side, back corner.
Mine has one of those combo water dish/hide things that is on the cool side. She poops behind that. I put paper towels there and she wouldn't go on the paper towels. Apparently mine likes a smooth surface to poop on, because when I first got her I used paper towels and she would poop on the lid of her moist hide. Then when I switched to slate tile, she started going over behind her water dish... *shrug