The two most common (forked F, and the one that's fingered like E plus the extra key between E & D) will be your best bet. Even if your oboe has a left F key (a 4th key above the usual 3 for the left hand pinky), it will only be marginally easier, if at all.
Am I right in guessing that your problem is being able to leave your right hand pointer & ring fingers down (for the forked F), while moving your right hand middle & pinky fingers at the same time (to play the C)? If that's the case, the bad news is, you don't have other options, and will just have to practice it until you get it smooth.
If you just cannot get the coordination (at least before audition), and the problem is causing you to accidentally play a D in between the C and the F, try to make the C key close just a fraction of a second before your middle finger key (when going from F to low C) and make the C key open a fraction of a second after you lift the middle finger (when going from low C to the forked F).
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