Actually, the small box gives the biggest chance for daily buildings, because it gives more rerolls (additional boxes; that's because they have a higher chance for hazelnuts).
OK, you're right. My bad. I hadn't factored in at all the fact that you have a better chance of receiving more free nuts comparitive to the number of nutshells opened when you go for the 50 nut rolls.
To satisfy myself I did my own calculation on the probability here. I worked with a starting point of 6,300 nuts, purely because it's the lowest common denominator of 50, 90 and 140 so it seemed a tidy place to start. With these number of nuts you will open the nutshell:
Small = 221.9 times
Medium = 102.5 times
Large = 58.4 times
Thus giving you the probable chance of winning this many daily prizes:
Small = 15.5
Medium = 13.3
Large = 14.6
It's all very minimal, either way. Given that the most nuts you can pick up is in the region of my previous calculation of about 5,286 then you would need to be playing with the whole month's worth of nuts, having collected everything, to statistically give you a chance of having one more daily prize from the small nutshell than from the large nutshell.
Nonetheless, apologies for my previous mathematical blunder.