Mage - When to use which pet?

[Odeseus]

For leveling, make sure you get the torch focus ASAP and then use fire pet until you are well into your 50s. Really no reason to use anything else.

Mid 50s get interesting. I used 49 mage pet until 56 when I got the "Decoy" pet. I'm 58 now and generally use 57 earth pet, although the "Decoy" pet is just as effective in most situations. Just a personal preference.

Earth pet has slightly better defense (mostly because the summoned pet is higher level) and much higher DPS than "Decoy" but worse DS and higher mana cost, particularly since you have to cast DS yourself.