I've just bought our first robot - an LG VR6270LVMB - and am really pleased with it.
We have a large, open plan house with a lot of obstacles (and two cats), and mostly timber floors. It was the large open spaces that lead me to choose the LG over the iRobot
- random sweeping wouldn't have worked well in the environment. When it does get on to our few carpeted areas, the robot switches to turbo mode and does a pretty respectable job, I'm constantly surprised by the amount of dust it collects, despite running on a daily schedule.
The other factor is the noise, or lack of it. We have a 6 week old, and the LG is quiet enough that it can vacuum his room while he's asleep, and he doesn't wake. It's also more cat-friendly because of the lower volume.
The only issue I've had with it is that it doesn't leave much in the tank to get back to the dock, and as such it hasn't made it back to recharge and continue as of yet. I've changed from zig-zag mode to cell-by-cell for the next clean, and hopefully this will result in a more efficient result.