I like CE3's, but there are a few negatives when compared to cartos. They can leak if you are unlucky. They need to be cleaned out every once in a while. Even then they build up with gunk on the coil. I had 2 prematurely die I think because I did not clean them out properly.
The cartos are made of steel. Flavor is not as strong, and I feel like I am sucking through cotton when I vape. They are basically bulletproof, no cleaning, filling is easy, and I have never had one leak [unless I fill poorly].
Even with the negatives, and the extra work in cleaning them out, I prefer the CE3 just based on the strength of the flavor and vapor production. You are effectively using more juice per hit. But it is the best I have tried as a newbie. [CE3 > x2 clearo > carto.]
That said, for my sister, I just ordered her a ton of cartos. She wants to try e-cigs, and the definitely liked the CE3, but did not like the work that goes into it.
If you want easy, cartos are the easiest to fill, no cleaning, and durable.
If you want the best vape, CE3 cannot be beat.
Definitely try them all, find the one that works best FOR YOU, and stock up!
EDIT: I am not as experienced with the x2 clearo. As I said above, the hit is not as good as a CE3, but still good. I have only refilled mine twice so far, and will clean it out once the tank is near empty. So many toys and juices to try out. I think it's half the fun.
