We thoroughly tested the iRobot Roomba 650 last year, and while it wasn't gentle, boy can this thing clean floors.
Navigation is everything for a robot vac. Where the device can't go, it can't clean. The 650 will barge into tight spaces, attempt to summit high carpets, and roll right over inch-high obstacles in pursuit of that last gram of dirt. On the other hand, if your living room is dense with handcrafted furniture hewn from the finest mahogany, you can be sure this overzealous Roomba will scuff the heck out of it.
But if you're rocking IKEA furniture like the rest of us, the iRobot Roomba 650 is one seriously thorough robot vac. Plus it includes conveniences like auto-docking and recharging, not to mention a seven-day customizable cleaning schedule. $318 is a great price for all you're getting.