The rest of my life trapped in cramped conditions living on strict rations with a large number of other people, constantly haunted by the knowledge that if the radiation doesn't sterilize us all before we make it to the heliopause, anything built by the lowest bidder will never last any longer than it takes those responsible to be safe from consequences?
Most likely whatever is optimum for a minimum viable population. I haven't calculated the ideal ratio, or the number of people needed aboard this ship.
For a generational ship, 1:1. For several reasons:
1. Population stability is the goal while in transit, not growth. There might be room on the ship for growth, but the food production capacity and long term supplies are strictly finite.
2. General societal stability: Most human societies that practice imbalanced mate sharing in either direction have suffered conflict as a direct result. Communal living might make sense in the situation than traditional family units, but that still means an even split.
3. Any gender disparity will be erased in the first generation anyway.
For a sleeper ship, now, where the initial passengers wake up at their destination, things get a lot more fun. You can plan for population growth in this scenario, which can mean a male:female ration in the 1:2 to 1:4 range.
The entry barrier for this kind of colonization is a lot higher, though. Everyone who boards a sleeper ship has to be physically and mentally up for the task of building a colony. A generational ship has the luxury (and potential danger) that the population that arrives at the colony will be so far removed from the one that boarded the ship that it almost doesn't matter.