Hi
I use both carto tanks and the Protank. For me, in my experience only, the carto tanks win for flavor; the Protank wins for ease of use, however, not significantly. One of my carto tanks (from Valley View Vapes) has a side fill screw, which makes filling just as easy as with a Protank, and using a "tank tool" makes filling a regular cart tank pretty much a breeze, but it takes a little practice - just a little. Most of my tanks as from IBTanked. I use Smoktech, Boge and IKenVape cartos.
The biggest drawback with cart tanks for a lot of people is learning how to prime a carto correctly. Again, it takes a bit of practice, but it's not hard. Math is hard, prepping a cart and keeping it filled isn't rocket surgery. I can prime a carto and fill a tank in under two minutes, including letting it sit for awhile to let the filler get completely soaked. I don't remember the last time I had a dry hit.
The Protank is easy to use in the sense of fill it up and forget it, but I've found it fussy when it's cold and tends to leak periodically. It also leaks when left tilted, I don't mean on it's side, I mean at about a 40 degree angle, which annoys me because I often leave my mod sitting in my lap. It also has a airy draw, which I'm not crazy about, but have gotten used to. People have solved these problems by restricting the airflow, using EVOD heads instead of Protank heads or pulling out part of the wicks or whatever, but I got Protanks to "plug and play" and I don't like messing with them. I often get more consistent performance from little clearos if I mess with them. Again, this is just my experience. I'm sure at least one person is going to tell me I don't know what I'm doing - whatever.