Since no one else has answered this yet I'll give it a whirl.
I can answer only from what features are on my car so perhaps someone else will say differently. Porsche Connect gives you, among other things, the center console USB port which does CarPlay. For me that's the big win. It also gives you a data source for Porsche's Navigation and a few other things. The general opinion is that Navigation is not as good as the real-time systems on a smart phone. So if that's what you are asking about, go with an iPhone running CarPlay and your choice of navigation programs. Your car may not even have Navigation even if it does have Porsche Connect.
When the PCM detects an iPhone on the USB port it will ask you whether to use it as an iPod or an iPhone. iPod lets it play music and stuff but not do CarPlay. Be aware that if you have another phone such as Android which already connects with the PCM by Bluetooth to do hands-free phone calls, the PCM will drop that Bluetooth connection if you select iPhone.
The USB-port iPhone can be one in service with your phone provider or it can be decommissioned. If it is not in service you can make your Android a WiFi hot spot and let the iPhone get its data from the Android.
