I'd say it depends on kill speed, and comp. If you're running with a DPSing WHM, Radiant Shield can actually be pretty garbage in trash pulls since it won't work for roughly 10s out of its duration. On the other hand, if you can kill stuff before you have to re-Bane with Ifrit, might as well take Ifrit.

Garuda is by far the safer trash pull pet though. Quicker Shadow Flare and Bane, and as long as you kill before a re-Bane then the extra Painflare you'd get can really pay off.