From experience, I would definitely not be inclined to go with the cheapest, flat rate fee option servicing the area.
I'm probably not much help with recommendations as I have 2 IP's a bit further out on the northside so I'm not sure my current PM's would cover that area, but I can PM you details if you want. I have recently heard of one called "Living Here Wilston" who seemed to be a smaller PM-only agency with some experienced staff...don't know much about them, but from what I did get told I would be trying to find out more if I had an IP in that area. I'm sure there are others with recommendations too...