I found Fiocci to be the dirtiest ammo... But many like it.
Underwood is one of the absolute best ammo IMO, better than mass commercial brands as it is close to spec (1500ft) .357Sig and better spec for .380 otherwise Speer is very reliable a consistent.
Have a few boxes of Sig ammo left, amazed how they have pretty much abandoned their own design (.357Sig) but hey... Used to get reloads for that but lately have just kept all the Brass (once fired) in case some day I have to reload it to shoot, but for now will keep buying the round as needed. Range and Carry is the same, want predictability if ever needed!
Good Luck