PSoC3 and PSoC 5 share the same resources, (nearly) no difference between them but the PSoC3 has got an old-fashioned 8055 CPU core, while the PSoC5 has got a more modern ARM M3 core.
PSoC4 has got some different resources and a much cheaper ARM M0 core. Some family members have got BLE
PSoC6 is unique; there will be two cores, both ARM, but different ones.
So as long as you are staying to low volume productions / prototypes and do not need BLE, the PSoC5 can be your choice.
Bob, thank you for the explanation.
You are always welcome!