I would use Vector for melodies on a rhythmically quantized grid, whereas Hermod is very useful if you want to play/record more loosely timed melodies or notes.
Vector plays steps whereas Hermod plays midi events, which are not necessarily restricted to certain steps.
As for drums I prefer Vector. Together with a Launchpad it’s super easy to program and change drum hits. And with the upcoming 2.0 firmware adding random elements, muting drum voices, etc. will be super easy.