From the Martyrologium Romanum (which you readers can put into perfect yet smooth and elegant English):
Memoria sanctorum Angelorum Custodum, qui, primum ad contemplandam in splendore faciem Dei vocati, a Domino etiam apud homines commissi sunt, ut iis invisibili sua, sed sollicita, praesentia adessent ac consulerent.
Because angels are not limited by matter, since they are purely spiritual persons, each angel is his own species. They are like in that they are angels, and unlike in that each one is particular to himself. There is, therefore, a hierarchy among the angels. But all of them always contemplate God, as angels can. They don’t have to be limited to any place, since they have no bodies. They simply are where they are in action. So aligned are they with the will of God that when they appear in Scripture and speak, sometimes it is hard to tell when God is speaking and when they speak.
Our angel guardians can be from the anywhere in the myriads and myriads of ranks of the angels. They could be from the highest of the high or even from the lowliest little angel at the bottom of the hierarchy. But even the lowliest of the angels is beyond any human conception of mightiness. The least of the angels, were God to will or permit, could mash the cosmos into a little pea and flash the Big Bang again. Provided that it falls within God’s will, from which it is impossible for them to stray, the material universe presents no obstacles to them. They know the essences of things directly, without having to figure them out.
Do you pray to your Guardian Angel? I sure do. I am constantly asking for help with problems and, especially, with other people. I will sometimes also ask the angelic guardians of other people to help me work something out when there is great need.
Even though I loath the pastels and the rather foofy portrayal of these fearfully beautiful beings, I love the old pious images made for children’s bedrooms of an bright and obviously invisible angel preventing some distracted little kid from plunging off a cliff as she tries to pick a pretty flower that is just out of reach, or guiding children back to a safer path. We all all get into trouble and we all need this help.
God, who knows us better than we know ourselves, sends us mighty help before whom the fallen angels of Hell withdraw in fear.