Cartomizers - the most popular for EGo are Boge LR 2.0. I use the Boge standard resistance because I move them between slim 510 and Ego (slim batteries are not supposed to use LR - it can damage the batteries). The standard resistance may be easier to learn on - they won't singe as quickly if you don't keep it damp enough. The LR ones will use your battery charge up faster. Remember to fill these fully - I make them take 18 drops, then wait 20 seconds, then however many more drops it will soak in, while holding something against the threaded end hole - aim for the stuffing or inner wall. Then clean it up well. Then let it lay on different sides for 15-20 minutes to make sure every bit of stuffing gets wet. While vaping, if the vapor seems a bit dry or a bit light or tastes a bit off or if the carto is unusually warm, take it off the battery and add juice. I usually replace the white soft cap with a plastic drip tip on my main pair of cartos - cool comfortable mouthpiece and easy to remove to add juice (I do not drip into it - the carto has a center air channel).
I find that for me, thin clear juices help my cartos last longer. I use 20% or less VG and juices that leave little or no flavoring sediment.
Benefit of dripping - I drip juices that I am just testing (only juices I love get cartos). I drip juices that didn't quite earn cartos, and juices that are thicker than what I want to use in cartos. Dripping gives good vapor and flavor.
Benefit of cartos - keeps my favorite juices ready-to-vape and SEPARATE - no mixed flavors since they each have their own atomizer. The juice generally stays where it is supposed to. I hardly ever have to clean my atomizers.
Atomizer + cart - useful for new vapers. Simple but flaky, prone to leaks and juice in the mouth. Occasionally I use a Joye 306 cart w/ blue foam to hold a juice too thick for my cartos that I want to vape. A Joye 306 atty plus Joye 306 cart together are the same size and appearance as a Boge carto. But the Joye 306 cart sometimes gives a bit of plastic taste and its juice cup is small. (510 threaded devices can use 306 atomizers. 306 atomizers need their own style drip tip and are what I often drip on - they are easy to blow out).