Chronos. There is rarely a reason to get anything else for Jenos except Chronos if you're intending to heal with him. If you find yourself being hard-countered get Chronos II then buy another item to properly defend yourself.
Recently, Maeve's Midnight was heavily nerfed - it can be countered by Resilience (at the time of making this) and go down to a minimum duration of around 2 seconds. If the option is available to you, buy Resilience - especially if you're her target.
While I generally recommend Agony in the event a Ruckus is present, if you find yourself alone against a Ruckus at full health then that small time won't be nearly enough to kill him. Just shoot him, Rend Soul, and use the stun time to get out.