The P series is new, so far only confirmed to be coming out in China. In the US, its:
Z series (I'd say the X series is about equal but I think it's discontinued now)
G series
E series
The Z series and G series also have the Play or Force models, those are the low end of that series. Current US flagship for Moto in the US is the Z3, I think at least for carriers its a Verizon exclusive. The Z series use a system called
Moto mods that has an accessory connector on the back of the phones that can be used for things like batteries, camera (Moto makes a Hasselblad camera mod with a physical zoom), and even a projector. The Z3 will use a Moto mod for 5g when it goes live for Verizon in their test markets. It has a different modem chip in it compaired to the phone and will only do 5g data while the phone does the calls and 4g data.