Maybe your hygrometer is messed up. If they get wet they start to give false readings. Did you try a different one?
Tubs aside, I think the first would be a better option. Ball pythons can stress out in an enclosure that is too big, and a tiny baby is even more prone to stress from a big enclosure. A 3' long enclosure might be good for a ball python pushing 2,500g but surely not a tiny baby like yours. The smaller one will last you a long time.