At this point I’ve had the opportunity to try Roomba, Neato, and POWERbot, so I thought I'd share my experiences with them. Of course, YMMV. For all of them you can program to clean at a specific time each day, or vacuum on demand. So they all have that going for them.
Roomba 860: A neighbor let me borrow his new Roomba to test it out, which is what started all this. It is okay, but not great. The method it employs can be best described as that of a really good housekeeper who did a few shots before starting up the vacuum. :) It got the job done but the route was more entertaining than efficient. I didn’t get to try it out over multiple uses so I don’t know if it would lose suction if not emptied daily, but from the way it’s built I’m guessing probably. The bin was easy to empty though I can see large furballs and dustbunnies getting stuck in there pretty easily. The noise level isn't bad, but it would be irritating if you were trying to listen to a phone call or the television.
Neato D80: This was better than the Roomba for cleaning. It maps out a room, vacuums all around the edges and furniture (though still bumps everything), then goes in rows until complete and onto the next room. As long as the door is open it will go in there. It managed the whole ground floor of my home on one charge, no problem. The one issue was that if you don’t empty the bin after each and every use, the next time the suction suffers. The bin is easy enough to empty though so not a major deal. It was louder than the Roomba, and because my entire ground floor is hard flooring, a combination of bamboo, tile and stone, it made this really weird noise like squeaky sneakers as it cleaned. I didn't try it on the carpeting upstairs given how much the suction suffered after one use downstairs so I can't say how it is on carpet.
POWERbot R9250: This is the one I ended up getting after returning the Neato, and I’m very happy with it. It is more expensive but is solidly built like a regular vacuum cleaner. The Roomba and Neato felt like toys in comparison, like if you kick it or trip over it you might break it, the POWERbot however might break your toe. Or at least make you spew some creative expletives. This one is really meticulous in the way it cleans! It goes in rows and goes right up to the walls and furniture but doesn’t smack into them as heavily the others did, but will occasionally bump something lightly. I don’t have much use for the wi-fi right now, but may later. On regular clean mode it is still quieter than the Neato (this was a huge deal for me since I work from home and need to be able to hear meetings) and in regular mode it's probably on par with the noise level of the Roomba even though it’s supposed to be way more powerful. There is also a power mode, which is marginally louder, and a quiet mode which could vacuum around you while you’re on a call or watching TV and not make too much of a noise problem (and that's on hard bamboo flooring, it would be even quieter on carpet). With my home I’ll probably never need it to since each level doesn’t have a ton of floor space, but if it runs out of battery before it is done it will go back to the charger to recharge then pick up where it left off. It has the largest dustbin of all of them, and because it’s built more like an upright supposedly won’t lose suction if you don’t empty it after each use. It also comes with a remote you can use to guide the vacuum to where you want it to clean, then point at the spot you need it to work on. The one drawback on it that I noticed is that if you run it on max clean (which makes it vacuum over and over until the battery runs out) it seems to have difficulty finding its charger if it is in another room. It kept trying to go directly to the charger only to realize there's a wall there and then tries from another angle. I'm sure it would have eventually found the charger, but I took pity on it and carried it home. The next day I tried it out upstairs, where it easily went under the beds and tackled dust bunnies that likely predate at least one of my pets. No problem whatsoever. I then recharged it and set it to clean downstairs, to see if it loses suction with the bin not being empty (it was over half full). It still picked up all the stuff on the floor, with no problem. Once it was done I emptied the bin and it was pretty packed, so this is not one you will have to empty before running it.
Overall they were all good and they got the job done. But the POWERbot is the one I will keep and the one I’d have no qualms about recommending. It is a little taller and wider than the others so may not fit under some furniture in all homes. In my house that's not a problem as most furniture is 6" or more clearance, so ample room for the POWERbot so it gets under beds, sofas, and most tables. It is too wide to go under the dining room chairs or breakfast bar stools, but those are easy to move if I want a more thorough cleaning in that area.