You are looking to buy anAudio interface for use with Garage Band? If so the first thing to do is list out what you are going to connect to the interface. Is it microphones (how many?) a guitar, digital piano? do you need MIDI.
Little things like headphone volume control separate the monotr volume and if the jacks are on the front or the rear of the box.
Once you figure all this out which brand to buy is easy.
BTW Why are you limited to just those two? These are so many others