Everyone definitely has favourites, and they're different person to person, so occasionally it's difficult. But so far zero "foster fails" (i.e.: we haven't kept one instead of getting them a "forever home"). My wife does all the hard work, and gets regular comments that the grown cats she's responsible for are always of excellent temperament, and a great with kids, adults and other pets. Plus the social media effort she does means people frequently contact her direct, and the kittens find a home often long before our portion of the work is done (i.e.: getting them up to health and weight for de-sexing, which the RSPCA does at their cost before people adopt them for good).