If PSoC4 satisfies project needs, and you are already familiar with it, use PSoC4. In the production environment the choice of the microcontroller is dictated by the cost, and price difference between PSoC 4/5 is substantial.
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To add to BoTa_264741's point, PSoC 4, specifically the PSoC 4S series (4000S, 4100S and 4100S Plus) devices have the latest CapSense IP that provides additional features along with improved sensing algorithm.
Therefore, PSoC 4 would be a better choice for the application.