I highlighted the winner in each of the categories. For fat content, I could not decide on a winner. Culturally, fats would be something to avoid, but given that I have lost a fair amount of weight this year, I am not overly concerned about taking in too much fat.
There is another difference in the size of the pieces not accounted for in the chart. While there is clearly more mass in the M&M's bag, the Reese's Pieces come in smaller pieces. I have read about a psychological effect on portion size. If you cut your food into smaller pieces, you will get full faster and eat less. So, it is possible that if I eat the Reese's Pieces one at a time, I will likely feel more full than I would if I ate the M&M's one by one.
Something going against the Reese's Pieces is the thinness of their candy shells. I discovered this by accidentally dumping the crumbs of the Reese's bag on myself. After eating the bag of M&M's, the container was empty. The Reese's contained at least a gram of chipped up shells; this would likely increase the discrepancy between the weight of what I actually eat from each bag.
On the other hand, Reese's Pieces are the original peanut-buttery bite-sized candy. Should I not reward creativity over imitation? Then again, shouldn't I encourage innovation (Apple's Lisa came first, but I still prefer Windows)?
Hershey (Reese's) is a publicly traded corporation [Hey man, the corporations are ruining American, man], while Mars (M&M) is family owned. On the other hand, Mars' revenue is an order of magnitude higher than Hershey's (about ten times as much), so I shouldn't I be helping out the little guy?
The girl (Green M&M) on the M&M's bag smiles at me; I like it when people smile at me. Reese's make me smile because I think of Officer Reese from Family Guy.
Conclusion: Life is full of hard choices.
As an aside, yes, I noticed the line "Weight (g)" in the table. I apologize to anyone that ever passed a science class. Also, it says "Reese Pieces", I should have used the possessive. Time to get a snack and then back to homework.