So *obviously*, it varies depending on the creature and the type of saving throw being invoked, but as a general rule of thumb, attacks tend to land more often than saving throws will fail. This boils down to a couple of factors:
- Ties always go to the person performing the action. So Attack Rolls will succeed when the roll matches the AC, but Saving Throws will succeed (meaning the effect fails) when the roll matches the DC.
- Methods of gaining advantage on attack rolls tend to be more common than methods of conferring disadvantage on saving throws