In current (115) version scrap generation rates are:
sticks = 0.00
other = 0.08
Basically this make blocks like cobble dirt and netherack super effective for recycling.
My suggestion is simple, 1% recycle rate for:
Stricks (this will allow to recycle 8 sticks with same overal chance as log).
Netherack
Dirt
Leaves
Sand
(due instantmine with diamond drill)
Cactus
Reed
Wheat
Seeds
(due ease of autofarming)
Also its possible to recycle smpIC credits (coins) but due halfiron cost it is not problem.