Un-PC to say so: but so far the evidence is that kids do better with biological mum and dad at home. In particular there's quite a lot of evidence about absent dad and it's not positive. The evidence re step dads isn't great either: much higher rates of child abuse. Not yet enough evidence to say whether same-gender pairings have the same benefits as mom and dad.
Of course evidence also says that 30% of kids weren't sired by the husband bringing them up thinking they're his- so as always there's stats to be cherry picked for every viewpoint. ;-)
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
