I'm running 5.3.1 live and found that with my lcd monitor, I got much better looking fonts by forcing the system to use anti-aliasing. In the KDE Control Center > Appearances & Themes > Fonts, I changed the default for anti-aliasing from "System Settings" to "Enabled". I didn't do any further configuring there.

The other thing I do as a first step on any Debian-based system is to just say NO to bitmapped fonts.

Code:
sudo dpkg-reconfigure fontconfig-config
I accept the defaults presented about hinting, but at the last question, I say NO to Bitmapped font support.

Ah, much nicer. Even at non-native resolutions, this helps out quite a bit - at least for me.