My understanding of the labors/athlos was that there were always supposed to be twelve and that they weren't to purify him from the murder of his family, but to atone and earn his place as a immortal on Olympus (hence, I thought, why there were twelve labors because of twelve Olympians):
Nemeian Lion- Dionysus (lions were sacred both to Rhea and Hera, but also to Dionysus - as well as leopards, this one was "king" and apparently reared by Hera the offspring of Selene or else of her son Typhon or grandchildren Orthus/Khimaira; also you'd have to be kind of mad to strangle a lion invulnerable to weapons, Herakles lost a finger from this one too)
Hydra Lernaia- Ares (although reared by Hera, serpents were a animal Ares favored, he mated with Demeter/Tilphousia to create the Ismenian Drakon, serpent of Thebes - and it was by the teeth of this drakon that Spartoi warriors were sown and grown from the earth)
Elaphos Kerynitis- Artemis (the golden hinds were sacred to her, four of them drew her chariot, the fifth was the one captured)
Erymanthian Boar - Zeus (before this labor, Herakles was a guest of a centaur Pholus - hospitality to strangers was one of the better things Zeus was god of, who told him how to capture the boar, but died as a result of the arrows Herakles used to kill the centaurs who became maddened by the wine Dionysus gave as a gift- the boar came off a mountain, pigs were sacred to Demeter, Hestia, it was either sacred or offensive to Aphrodite, Apollo used the blood of a pig to purify those at the Delphi oracle, boars also had something to do with Ares - he is said to have turned into one to kill Adonis, but also with Artemis - she sent the Calydonian Boar, they are also mentioned being scarified to Hera and Hermes; most likely it was a animal that all the gods had as sacrifice.)
(in one day clean) Augeias' stables- Athena (he rerouted the rivers Alpheus and Peneus - how? Well, Herakles doesn't seem to have had anything to do with their daughters so maybe by vowing that he'd not touch them)
(Drive off the) Stymphalian Birds- Hephaestus (although they are identified with the Birds of Ares encountered by the Argo crew near a shine of the Amazons and said to be raised by Ares, Athena got from Hephaestus some 'bronze noise-makers' which was the only thing to drive them off)
Cretan bull - Poseidon (Poseidon gave the bull to Minos and the Minotaur resulted in it's union with Pasiphae)
The mares of Diomedes Thrakios (the Thrakian) - Demeter (as "Tilphousia" mother of the horses of Ares by Boreas; mother by Poseidon of the immortal horse Arion)
Belt of Hippolyte (Amazon Queen) - Aphrodite (it is called the girdle of Ares, but Aphrodite is more famous for her belt and Admete is sometimes said to be a priestess of Hera who sometimes borrows the belt of Aphrodite too; also Hippolyte would go on to marry Theseus)
(Red Coated) Cattle of Geryon - Helios/Apollo (the help of Helios was absolutely necessary in getting to Geryon's isle, Herakles got Helios's attention by archery I think, and killed just about everyone on the isle other than the cattle and Geryon's daughter and when Herakles encountered Geryon's sister Echidna he had three sons by her: Agathyrsos and Gelonos and Skythes - the only one to have Herakles bows and belt, the other two being cast out; Apollo was the protector of boys/men, and was the one that killed them too - as Artemis did for women/girls)
Apples of the Hesperides - Hera (the garden that the Hesperides guarded was hers, a marriage gift of Gaia)
Fetch Kerberos - Hermes (Herakles had help by both Hermes and Athena - and Persephone/Hades in this task, but as Hermes was the god that guided the dead)