>>96082631
Ruffian is the only time a rogue subclass wants to change their key stat off dex. They have access to medium armour and can use it for accuracy. That said, if they focus on throwing they might want to key dex anyway.

As for how good they are, they're both great. I think ruffian can be more engaging in a fight due to maneuvers but thief can really go hard on boosting any mental stat they want without losing anything and you can do funny stuff with that.