I actually like Jack when it is concerning latency and think it is a good system. BUT it is a pain.
I used 2 separate sound cards. One is a Pro level I/O breakout box that Jack controls and the on board sound card is controlled by PulseAudio.
Here is the focusrite help page dealing with latency and what you must turn off for recording. https://support.focusrite.com/hc/en-gb/articles/207546515-Op...
It will also support JACK but for quickly getting up and running it's about the simplest DAW I've setup on Linux configuration wise.
Not open source but I give them lots of kudos for supporting Linux from the start.