I am the sad forgotten middle child.
I have three brothers. Oldest is 9 years older.
Special PFB, can't really begrudge him that for many reasons.
Next is 18 months older - bad childhood asthma in and out of hospital and needed lots of extra parent time.
Younger brother unexpected unplanned whoops. Very loved by all.
I think being the only girl was also a huge disadvantage. Again for many reasons. My Mum was better at boys and my dad is just rubbish so... Well that's a short version. 
But I think three is good because you have a peace keeper, usually one will fall out with one other so there is someone who can help with a middle ground mediation.
But nothing splits easily three ways. 
I don't know. I think that if someone could give me a 1 yo child and I didn't have to do the pregnancy or newborn bit I'd prefer that
I haven't made my mind up. I haven't spoken to DH about it for a while. I would imagine he is still set on just two.
This weekend has seen some better sleeps. But DS is still getting up between 5 and 6. Which is not easy. DD has started sleeping longer, until about 6:45. I guess because we take DS downstairs. 