I've used Polytek's Platsil Gel-10, which is ok for a fairly skinny body. I prefer a softer silicone, like Smooth-On's Ecoflex 00-30 to get more flexibility for facial movements though. Or if the body is a bit thicker. Since I had both, I found painting on the skin with the Gel-10, then filling with the softer Ecoflex, worked well. (They are compatible with each other - you can even mix the two brands.) Ecoflex is also a bit runnier so it pours more easily. That was helpful when filling a body mould through a thin neck opening with neck wire in the middle. Gel-10 clings to the sides of the mould better, though all the silicones I've used will slowly run down and pool in the bottom, so you can only paint on a really thin layer at a time and build up 3 or 4 layers.
I also have some Platsil Gel-00 which is softer than the 10, Says it's a 00-30 same as the Ecoflex, but haven't used it yet.
In the Shore A hardness scale, smaller numbers mean it is softer, so 10 is softer than 20 or 30, which are really only suitable for making moulds. So the 0 would be at the bottom of that scale. The 00-30 is a different scale, and I'm not sure whether the numbers go in the same direction, or in reverse like minus numbers, so 00-30 would be softer than 00-20. Either way, 00-30 is the softest I've used.
All the ones I've used are platinum cure silicones, and can be very fussy about what materials they come into contact with (especially sulphur), so I have to sculpt with Non-Sulphur Plasticine, and never cast latex in the plaster mould and then try to cast in silicone, the traces of silicone will stop it curing. But if you sculpt in Chavant NSP, Monster Clay, or Klean Klay or any other non-sulphur clay, you can make a mould in Ultracal or Hydrostone plaster, or in polyester resin fibreglass, and cast Platinum cure silicone in it.
There are Tin Cure silicones that are soft enough for makeup FX and puppet making available in the US and the UK, but not where I live (Australia). So I haven't used any. The silicone bodies in Corpse Bride would have had to be tin cure, because they first cast in foam latex (for lightness), then trimmed it back and cast again in silicone over the top of the latex. With platinum cure, the silicone would have stayed runny forever from contact with the sulphur in the foam latex.
I'm using Platsil Gel 00, and have found this works very well for bodies, although it is not as runny as Gel 10. I used Gel 10 to make a head piece (full-size) for a theatre production of Frankenstein, and a single piece, 6mm thick, was used for over 40 performances! By the end it had stretched a little, but it shows how tough this stuff is.
Where I am still having issues is with eyebrow paddles, because even the Gel 00 bounces back too much. I have yet to try Nick's method, and am thinking of adding quite a lot of deadener to see how soft it can go. May just use 00 straight as the skin.