Which county should I file a complaint to be heard in the common pleas court?

I recommend filing in the county where the business is. This is because of the venue requirements in the Ohio Rules of Civil Procedure which generally favor suit in the same county where the wrongful act took place. Venue is proper in:  1) The county in which the defendant resides; (2) The county in which the defendant has his or her principal place of business; (3) A county in which the defendant conducted activity that gave rise to the claim for relief; (4) A county in which a public officer maintains his or her principal office if suit is brought against the officer in the officer’s official capacity; (5) A county in which the property, or any part of the property, is situated if the subject of the action is real property or tangible personal property; (6) The county in which all or part of the claim for relief arose; or, if the claim for relief arose upon a river, other watercourse, or a road, that is the boundary of the state, or of two or more counties, in any county bordering on the river, watercourse, or road, and opposite to the place where the claim for relief arose; (7) In actions described in Civ.R. 4.3, in the county where plaintiff resides; ( 8) In an action against an executor, administrator, guardian, or trustee, in the county in which the executor, administrator, guardian, or trustee was appointed; (9) In actions for divorce, annulment, or legal separation, in the county in which the plaintiff is and has been a resident for at least ninety days immediately preceding the filing of the complaint; (10) In actions for a civil protection order, in the county in which the petitioner currently or temporarily resides; (11) In tort actions involving asbestos claims, silicosis claims, or mixed dust disease claims, only in the county in which all of the exposed plaintiffs reside, a county where all of the exposed plaintiffs were exposed to asbestos, silica, or mixed dust, or the county in which the defendant has his or her principal place of business. (12) If there is no available forum in divisions (C)(1) to (C)(10) of this rule, in the county in which plaintiff resides, has his or her principal place of business, or regularly and systematically conducts business activity; (13) If there is no available forum in divisions (C)(1) to (C)(11) of this rule: (a) In a county in which defendant has property or debts owing to the defendant subject to attachment or garnishment; (b) In a county in which defendant has appointed an agent to receive service of process or in which an agent has been appointed by operation of law.