First thing I always did with any Numatic up to now was ditch the floor head it came with. The original style was OK on glued down commercial carpeting, but around the house I never cared for them much. Seemed to me that all the suction was focused in the centre, and they could be an absolute bear to push. Not keen on the way they sometimes flip up and lose contact on the backstroke either.
My preferred replacement was the Wessel Werk RD275, which most of us would recognise as the same head supplied with the Vax 2000/4000 series. One of the best I've used on hard floors, and worked well on carpets too without giving the user a workout.
The current head is more or less the same as that supplied with the Sebo K series (to get a stainless steel baseplate, you had to step up to the D series). Never thought there was much to choose between them, both performed fine for me with the only difference being the plastic version was lighter.