There are two guides I would like to recommend:
(1) Rufael Fitsum: firstname.lastname@example.org who guides in the Axum and Tigray region (and also took us to Danakil Depression).
(2) Girma Tilahun: email@example.com who is able to arrange trips all over Ethiopia (he is originally from Bale Mountains area) and accompanied us on a 10 day trip from Harer, through Awash and down to the Omo valley region.
Both these guides are fluent in English and demonstrated not just a wealth of information about the sites that we visited with them (delivered in an engaging and contextualised manner), but they also appeared to have excellent relationships with other local guides and hotel owners etc. Both were excellent at spotting and negotiating photo opportunities
Girma in particular appeared to be well known everywhere we went
Rufael also has a keen interest in birds.
By way of context, we (me and husband in mid thirties) were travelling on a private tour organised. These two guides were found for us by another agent in Addis who had organised our overall 22 day trip.