There is not a right or wrong answer to this question. I recommend you read this guide on property management fees.
I own a beach cottage in FL. The company that rents, manages (since I am in NJ) They receive 20%. They handle the rental end and also hire the cleaning service and oversees any maintenance problems.
I also have a multi-use building in NJ. One of my tenants manages the building for a rent reduction of $300/mo. He not only manages, but does the routine maintenance.
Find someone you can trust and ask other landlords around in your neighborhood what the going rate is.