If it’s for hard floors then it’s tough to beat a ‘freetime whiskers’. Effectively a bump ‘n’ go robot that will spend about 45 minutes diligently sweeping up detritus from your hard floor into its little dust store. Cheap on eBay and better than an expensive LG model.
If you’re a bit flush with cash then the iRobot models do hard and soft floors sufficiently to make a difference. though on hard floors not that much better than a whiskers, albeit nearly 10x more expensive.
The iRobot Scooba is a great hard floor washer.
None of them are a substitute for a proper vacuum cleaner, but they make a difference.