Cat, agreed.
However, if you leave it alone a lot and if it can't be let out, then you need two cats so there's always somebody to play with and the cat doesn't get bored causing it to develop odd behavior.
As for the sex of the cat, I'd suggest tomcats. If female cats get in heat, it'll get quite annoying for both you and the cat and the only way out is sterilization. It's a routine operation, yet much more invasive than castration of a tomcat.