i would look at it like this....
connection type (510 is the most common)
Battery LIFE (how long do you want your battery to last vs cost)
what to put the battery in...(again cost vs quality vs battery)
that is the steps i went through when i selected my first mod i went through and looked at all of them and settled on the 18650 because i drive a truck and really cant be messing with changing
batteries while driving. this brought me to the Silver Bullet it last all day and i dont have to mess with it and for the cost of a couple cartons of smokes i figured i wasnt looking back and was going to be spending the money anyway......lol
so first i wanted a 510 connector....
second i wanted the 18650 battery
third was what did i want on top
i settled for a dual coil
tank with a 510 connection that holds about 5 mil....
i wound up with the silver bullet and the map
tank and haven't looked back, of course you can go with the EGO's they just wasnt for me....maybe you can use these steps to help you decide what fits your needs best...