Personally I use Slick Honey grease, as to my mind, it's better in this application (seeing as my rear shock sits horizontally).
Float fluid for fox units, the oil gets moved around when the shock moves.
I've used all sorts, but find greases tend to get forced / pooped out past the main seal fairly quickly, rather than the teeny oil ring you normally get. And as LoCo said, ideally it needs to be moved about.
Fload fluid is a rebadged high quality automatic gearbox oil, so you can get a cheaper alternative (ebay Unipart Part 75W-90 Synthetic Multi Grade Gear Oil-0.5L) if you wish, but the cheap gearbox oil smells of ... cheap gearbox oil, and as so little is used (FF is great on door hinges BTW) you may as well get the real stuff from LoCo 🙂
Float fluid for me. Its ok valueif you buy a small bottle.