Which RTK system to use?

Hardware Other Hardware
1

I see few different vendors for RTK gps here.

This is a possibly new one to add: https://store.mrobotics.io/product-p/mr-m10020-a.htm ?
Any recommendation or comparison between the different ones ?

2

You are looking at the wrong page. Take a look at:
https://ardupilot.org/copter/docs/common-positioning-landing-page.html

That GPS is based on a uBlox F9P chip that is already supported by ardupilot.