I would say take the earliest flight in the AM , If F is fully booked there is a chance someone is out too late the night before and changes their flight or misses it completely.
Also look at what aircraft are operating that day ,
If there is a 757-300 , you have a better shot since there are more seats.
In my experience to SFO , i found it very hard to get an EUA unless I was on a full Y , but then again I never flew to SFO on a sat, always during the week or a sunday.