In mainstream Christianity, only Jesus is the Saviour, whom God the Father sent to the world to become flesh and blood to save humanity by dying on the cross. By necessity, the saviourSaviour has to be full human flesh and blood. This Jesus is also the Son of God, which is another requirement for the Saviour, but no angel is the Son of God.
In contrast, God assigns a different purpose to guardian angels, which is to care the people who will inherit salvation (Heb 1:14) after the Saviour saved them. The contrast is well taught in Hebrew 1.
Another distinction is from the service they perform for believers: Saviour saves us from the power of sin and the power of death (see Rom 6:1-11 and Heb 2:14-15), a service that angels cannot perform since angels never become human. Once saved, believers are still under attack from the dark angels although God somewhat restrain them, put them "on a leash" in a manner of speaking. Guardian angels are one of the means ofthat God uses to protect usour earthly life from the dark angels. Therefore the services are completely different.