Hmmmm.
My then 4 year old enjoyed both. But she LOVED meeting piglet! And, piglet was wonderful with her too! Plus, the atmosphere at Crystal Palace is worth experiencing.
BUT, you usually meet the Mad Hatter at breakfast in 1900 PF, which mattered to me.
The food had pluses and minuses at each, I would say, for me, 1900 PF was better, but, the kids probably preferred Crystal Palace, plus, if you are already in the park, leaving is a faff.