I am already using Moto G with stock Android, so want to experience custom Android.
Nexus series Smartphone are ready to go developer phone. There are many custom ROM (Android OS) available like CM11, MIUI, etc. All you need to do is, root the phone and flash the ROM. If I am not wrong, you can find an Window App, which does all in one go while your phone is connected to the computer.
I had Nexus 1, Samsung Note 1, Samsung S3/S4 and having Nexus 5 and HTC One M8. All rooted.