Re: Best saxophone for ballads...
Pete, that is a rather open ended question, because all saxes can play ballads. It is mostly up to the artist whether they want to use soprano, alto, tenor, baritone, or other sax.
What one do you feel comfortable with? And, the mouthpiece plays a big part in it too, having the one that gives the timbre you want.
I've used all of the above to play ballads. If you are already a sax player, why not just go with what you have now? After practicing ballads for a time, then you will have a better idea of what type of sax you'd want to use in ballads.