Ifrit has higher potencies but his attacks rely on your strength and attack stats. Garuda's attack has less potency but hers relies on your magic stat and int. Garuda's 100 potency wind blade will hit for 200+ while Ifrit's 120 potency move will hit for 120 and his auto attack for 60ish for me. Along with that his main attack is on a 4 second timer instead of a 3 second timer as it should be, so he lets it out slower. With both on Obey Garuda does slightly more dps (like 3-5, pretty tiny) but contagion weighs far too heavily in Garuda's favor for nearly every encounter.

Ifrit is useful in PvP though since he has an auto attack.