i use both…
i have knee/shin guards under jeans with textile pants over everything… the knee guards that came with the pants would move around too much for my taste…
it is a pain to put on the armour (but you could conceivably leave them on all day, not that uncomfortable). Armour by itself does nothing to stop road rash though, so if that is your main concern you will need to get some form of pants.
Additionally, I am guessing the armour’s straps would get shredded by the pavement and then you’ve got nothing 
