There are advantages to both
Atomizer + cart (or + drip tip if you use manual batteries which are more sealed on the end) - great for starting out, for trying new juices, for
vaping juices that are not something you vape often
Cartomizer - a bit extra expense but a fresh atomizer in every one, holds more
juice, needs juice added less often. You can totally switch flavors without cleaning anything. if you have a flavor that that is hard to get out of attys (like cinnamon) a carto is perfect. Compact and self-contained. With carto condoms on you can have a couple in your pocket. I think the big plus is not needing juice as often!
I think it's nice to own ecigs you can use both on, like 510 or KR808D-1 (can use a DSE901 atty or 510 atty w/ an adapter)