Within the city limits of St. Louis, I feel, is the safest. LE is not overly concerned about this activity in the city, so I would agree with the others regarding Forest Park. They do pay attention in Clayton, so I would not say I was staying there in ads, or in Chesterfield (West County).
Airport/Westport/Bridgeton can be sketchy, but as LM said, if you are screening well, and are not seeing a high volume of clients, any area should be fine. There are some very nice hotels in the airport area. I think the main thing would be not to advertise what specific city you are in, and let the client know after they are screened, or give them a mileage from where they are coming from, then let them know after they are screened.
Check the hotels, though, as some require hotel room key cards to operate the elevator which is obviously a pain for what we are there for (I know for sure there is one in downtown Clayton...I think it's the Sheraton). I do like St. Charles, but I know there have been some issues there of late. I also like the metro east (Collinsville/Fairview Heights, IL). But I give a general area and not the specific town in ads.
It is also helpful to get a 3 star or above hotel. They are usually bigger with more people coming and going and you don't stand out as much. Recently I had an outcall to a hotel in Collinsville that was not as nice as I would get (Comfort Inn). It was small, and the client was not well versed on discretion and behavior in the hobby. He came to the front door to get me after I had told him I was at the side door. There were four hotel employees at the front desk that he wanted me to walk by with him. I did not go in as I felt very uncomfortable and I left. First time I have ever felt that way or felt a need to leave a situation. I explained to him later why and he understood. But each situation is unique with hotels so do your research. But smaller hotels with not many people around do make me more uncomfortable.
This may be more information than you were asking for and you may already know all this. But discretion and screening keep you safest
Anything I can help you with please feel free to PM me! Good luck!