I think the lowest are Snickers, peanut m&ms and min 70% cocoa dark chocolate. I go for the dark choc as a little bit goes a long way to satisfying my sweet tooth.
The lowest just chocolate or chocolate coated nuts I think. Anything with sweet squidgy stuff inside will be higher because of increased sugar and fillers. In my Rick Gallop book it says to go for plain choc with high cocoa contect (75% or more).