garen and darius both lack gab closers
darius has better cc with his e while garen only has single target silence with his q
garens ult is an execute that scales with missing health, darius' ult deals true damage and has a reset that allows you to use it multiple times in a row if you secure a kill with it
garens passive is crazy health regen when out of combat so he can pop in and out of the front line in prolonged teamfights
darius needs to stack his passive on enemies to gain the movement speed and additional damage to his ult
imo darius is the stronger one of these champs in the current meta
garen is just so easy to play around, it really shows that he is a super old champ with an outdated kit that cant match the high mobility cc heavy new champs that are coming out now