You hear people talk about positive (maximize pleasure) versus negative (minimize pain) utilitarianism, or average versus total utilitarianism, none of which seem very satisfactory. For example, average utilitarianism taken literally would suggest killing everyone but the happiest person, and total utilitarianism implies what Derek Parfit called the repugnant conclusion: that for any possible world with lots of happy people, the total utilitarian must prefer another possible world with many more people whose lives are just barely worth living.

But really, it shouldn't be that surprising that there's no simple, intuitively satisfying population ethics, because any actual preference ordering over possible worlds is going to have to make tradeoffs: how much pleasure and how much pain distributed across how many people's lives in what manner, what counts as a "person," &c.