I'd recommend the Motu M4, or Focusrite Scarlett 4i4, for the loopback feature. The Motu M2, and Scarlett 2i2 are nice but neither offer loopback. With loopback for example, you can play along with a youtube bass backing track, a track that has all the music and you add your bass playing. Or play along to a backing track from your PC or whatever, and record your bass and or vocals or whatever along with it, and record it if you want to. I use loopback all the time, it's worth it to me. You could watch a podcast or livestream, and record it with the loopback feature. The M4 or 4i4 have more input channels also, but it you never use them, still worth it for the loopback feature.