Other than being the father or mohel, the highest honor at a bris is unquestioningly the sandak.
Beyond the sandak it really becomes a matter of opinion.
Some might call the "standing sandak" the highest honor. Though whether it was always called that or later called that to give similar honor to the honoree (such as the grandfather who did not serve as sandak) is a question for discussion.
Some might view placing the baby on the Chair of Elijah as a great honor. After all, if the presence of the prophet is noted and invoked through the appointment of this chair to such a role, being partner in placing the baby on this holy space is surely significant.
Some might view the speaking roles as most important - the recitation of the blessings and the paragraph in which the baby is given his name. Every other role at the bris (aside from the father and mohel) is a non-speaking and holding-baby-only role. If you view a speaking role as significant, then this one is pretty important (though the dramatist in me reminds all of the old adage "there are no small roles. Only small actors.")
The catch in this latter group of roles is that the speaker must be a fluent Hebrew reader, and insofar as the blessings go (from my perspective) the one saying the blessings should be an observant Jew - at least to the best of everyone's knowledge. These factors often leave the mohel as the default person for this role, or the community rabbi. At brisses for Orthodox families, this role might be given to a family member, or a friend who is more cantorially inclined.
My only recommendation is that whoever names the baby not be a person emotionally attached to the name being given to the baby. I have seen too many a grandfather lose control when the baby was named for a recently deceased great-grandfather.
On the other side, as well, one grandfather with "quite the sense of humor" got up to the part when the baby is named, gave the child his "Name, son of..." At this point, he is supposed to say the baby's father's name. When he took a longer pause, I thought in the heat of the moment he had forgotten his son's name. Turns out, he paused as if to say to his kid, "who is the REAL father?" People laughed good-naturedly (I think), but if I had to do it again, I would have had someone else name the baby.
Those kinds of jokes are not funny, and while the baby's father "laughed," I don't think he thought it was funny either. "My own father... Sheesh!"
Those kinds of jokes are not funny, and while the baby's father "laughed," I don't think he thought it was funny either. "My own father... Sheesh!"