I'm an only child and I'm perfectly normal, honest! *grin*

No really, do what works for you. If one is the number that chooses you, go for it. And go stick it to anyone who nags you for more. Mothers-in-law and grandmothers tend to be the worst offenders

As someone said further up, there's a LOT more couples choosing to have only one child these days, so its not like this is the 50s where you were weird if you had less than 4. You'll be boringly average.