Kryoflux is amazing. I have found the best way to get good images is to get a few different old floppy drives (you can find them pretty cheap on amazon or ebay) and take images with a few of them. You will find that each drive has different bad sectors in the images. You can then patch together good sectors from the different drives to create a full, complete image.

I was able to get a lot of disk images from disks that were failing to read fully on ANY of the drives, but were failing in different sectors.