I use a combination of Alpro knee pads, the Alpro kneeling pad and redbacks, depending on the job. The redbacks are really comfy and are great for jobs where you are moving around alot, in different areas,awkward small jobs etc. I mainly use the Alpro pad as it just sits there where you are working, i actually have two, one for laying, and another for grouting or sealing stone where you don't want to scratch the tiles. For big commercial jobs where you will be doing long hours the Alpro knee pads really help your knees out, but i never strap them up, as they just annoy me.
PPI is really important, and thankfully the old school days of being called a girl for not wearing gloves,knee pads and glasses and really important ear defenders have long gone.