A is the best, E the least efficient.
That's valid for all types of Upgrades and also reflects in their price.
Things get a tad tricky when you start comparing different Classes (i.e. a Class 2C vs. a Class 3D), but most fundamental figures are given in the lower right Corner when you just move the mouse over them.
Alternatively, you can always click on an item and then select "compare" to compare it to your currently fitted equipment.