Most of my mayors are near the docks and close enough to the cliff so villagers houses can't go in front.
I do have a extra player near the train station. It comes in handy when one of my other towns needs something.
The runs out and opens the gates. Retail is handy later on when you have an ABM. You can put it in the main room when it's high turnip price day or perfect fruit. Guest or you can quickly deposit the money.
I'd put it right by the left pond to be close to re-tail and the top of the map.
I'd advise against putting it by rivers bc i did mine that way and i deeply regret it.