Hi Korie, I will share my own feelings based on my experiences, okay, because someone else may feel differently
It's mostly a difference in vibration, or frequency. Angels are beings of pure Light, and closer to Source energy than any other being.
Spirit guides have been human, and have a deep understanding of how choices affect our outcomes. So they "guide" us by supporting us in making those choices that allow us to experience the brightest version of ourselves.
The angels, wholly loving and supportive, see us as the perfect beings of Light that we are and see that any choice is fine, and that we can learn from even the most negative of experiences. They may not necessarily try to steer us away from trouble because they are not judging it to "be" trouble - it's just another experience.
Every now and then I'll get a client who will say something like "Oh, my nana just died, and now she's my guardian angel."
Nana may have passed, and may be serving as a loving and supportive spirit guide, but it's not likely she's become an angel right after she dies. Angelic frequencies are just too far up there close to the pure creative Source Energy. As Souls, we are raising our frequencies gradually. Just like someone doesn't instantly lose 140 pounds, a Soul doesn't instantly go from a frequency of, say, 700 to 50,000. Right?
Animal guides are more of a collective energy of that species. And the animal ally (totem, spirit) is there to show you that you share in its qualities. You'll have both its strengths and weaknesses. In my own experience, connecting to my animal allies was far easier than connecting to my spirit guides! They made their presence known to me, and I understood it so much easier! And, we connected when I was child, and had NO IDEA what animal spirit medicine was LOL!!!
They all serve as guides, just differently. Anyway, I hope this was helpful