I really like the Huanuo Dual Monitor Mount: https://www.amazon.com/HUANUO-Dual-Monitor-Stand-Adjustable/dp/B08CXJPQG9/ref=cm_cr_arp_d_product_top?ie=UTF8

It's not the cheapest mount, but it works really well and being able to independently control each arm is a plus. It also comes with two usb ports on the mount for convenience.

I have two 32" monitors on mine, so if you ever want to to get bigger monitors, you will be able to.

For how you mount it to the desk, I don't think it really matters which way you do it; both ways should be stable enough. I had to drill a hole in my desk for a grommet style mount since I don't have a large enough lip on the back of it for clamping it to, and mine is holding just fine.