Checking the speed of Hard Disk(s) ?

I want to install Mojave on an external hard disk.

But I have to choose one - from those I have - that is fast (not the slower one).

So I am searching a free speed testing application for HD.

Do you know and use some ? TIA.

I use HELIOS LanTest for local and remote HD testing.

blackmagic disk speed test
https://itunes.apple.com/fr/app/blackmagic-disk-speed-test/id425264550?mt=12

You can use my LAN Speed Test app (made with Xojo). The free Lite version will do what you need.
https://totusoft.com

Aja System Test Lite on the App Store is another good Speed tool.