An atomizer is a heating element that has juice wicked onto it. When heated, it creates a vapor (not smoke). With an atomizer, either dripping with a drip tip (its basically a cartridge (cart) without any filler material in it.) A cartridge has filler material to hold "some" juice, but when the juice gets low in this, it creates a funny nasty popcorn like taste. These things require maintenance and refilling the poly fill, or using substitutes which you will read in here. look for cart mod in the search.
Cartomizers (Cartos) are basically a throwaway combination of the two above, and are built to not last as long as the atomizers. (atomizers are roughly 10 bucks, and cartomizers are less than $2) The biggest benefit is that it holds nearly a days worth of juice, especially if you alternate with 1 other cartomizer. There is also no nasty taste if you get the ceramic e2 cartomizers with version 4. Awesome vapor sells them. I love them, but some of my juice tastes better on the atomizer. I find fruity flavors and many subtle flavors taste better on a cartomizer.
I have an ego and I love it. dont pay more than $55 for a shipped kit. Make sure its genuine joye ego. I hear Rivas are great too. almost the same thing as an ego.
My ego lasts me 6 hours at least. I bought 2 kits to have backup chargers and batteries, and I am set now.