Aggravated Robbery is a class 1 felony. The minimum punishment for a class 1 felony is probation for up to 48 months. If a prison sentence is imposed the range is 4 to 15 years, unless the person is eligible for extended term then the maximum is 30 years.
Public defenders are lawyers, the court will determine if the accused is eligible for a public defender. If yes, one is assigned, the accused does not choose his public defender.
Not knowing your boyfriends record, if any, it is not possible to accurately assess what mandatory penalties are applicable.
As the other attorney said, it is a probationable class 1 felony. Depending on his background, he could get up to 15 years if convicted (and extended term does not apply). While there are many capable public defenders, he will not be allowed to choose which one he is assigned, assuming he qualifies. Your best bet is to retain an experienced criminal defense attorney. Most of us would provide a free consultation to discuss the case and the fee arrangements.
Several questions need to be answered here. Was a weapon used and/or carried. If a gun specification is indicted in Ohio a mandatory 3 year term is served before the robbery itself. Could carry 8 years (plus 3).