I remember thinking that the one with the lowest price would be the best bet. I would have been wrong. No big secret, but one that people do not often do. Comparing not only the prices but the sizes. Prices on products can be deceiving.
Coffee is a really good example.
During a recent grocery shop I had to decide between two sizes of the same brand of coffee. There were two sizes that were within my budget - 100grams and 150grams. To work out the best value for money I had to decide on a common denominator, which I could use to work out the best price. I decided on using the common denominator 50 as it both went into 110 and 150 easily. Obviously I decided on the larger jar.