As we can see, cakes are doing much better now, and sweets have improved a little as well, now challenging fruit for the number two spot behind chocolate. Biscuits now seem to be firmly at the back of the pack (no pun intended).
I have also created a chart demonstrating the spread between the best and the worst shake in each category (since I've tried exactly two shakes per category, I acknowledge that "best" and "worst" are somewhat shaky terms here, but never mind).
As can clearly be seen, although biscuits is the category from which the Worst Ever Shake was chosen, it can be argued that due to its poor performance and lack of range, breakfast cereal might in fact be an even worse category from which to sample. On the other hand, it seems that fruit for now dominates sweets, having the same upper bound but less variation, and chocolate remains in a league all of its own. Cake is the the most consistent category at this point.
Conclusions: avoid breakfast cereal and biscuits, and go for chocolate instead. With shakes, just as in life, chocolate reigns supreme.
 Or at least in situations where alcohol does not feature.