Hi LR, and welcome to ecf!
Is your question which lasts longer life-wise or which lasts longer with each refil?
If it's life, atties generally have a longer life than cartos, and the carts last almost indefinitely if you change the filler periodically. Cartos are considered disposable and therefore are less expensive than atties.
Cartos have a much longer
vaping time than atty/carts with each refill because they hold a lot more
juice. My 510 Boge cartos hold over 25 drops of
juice.
I use atties when at home because I always drip, but when I'm on a outing a couple of full cartos can hold me for the day.
Edit: Regarding your dealer question, I only get my blank cartos from VaporKing (boge not slb) for my eGos and Rivas. Other members more experienced with cartos can give more info.