I going with windows 10 home, my build should have a 2tb HDD and a 1 TB m.2 which should I put the os on
General practise is to install OS into a SSD.
I would probably put the OS on the m.2 drive. It should be an SSD, so it should be much faster than the hard drive for booting and program loading. The exception would be if you didn't care about boot and program load times and you needed as much SSD space as possible and couldn't spare the space for Windows or buy more SSDs, but that would be such a niche use case I highly doubt that would be your case (and you likely wouldn't be asking the question in that case).
Install it on the fastest storage device, so the M.2 SSD.
This topic has been moved from "Hardware > Other" to "Software > Operating Systems".
Oh, I'm sorry thank you for moving it