i have about 10 of the CE5's(CE4's with replaceable heads) i don't use the all to often i like larger tanks but they are great if i just want to vape a flavor for a few hours, they are not very pocket friendly im sure its why people report leaks with them,the tank is just held to the threaded part with a very light glue that dissolves with heat to dont try to boil them or clean with really hot water.
i also picked up a 5 pack of the CE5 redux's now those were total junk for me out of the 5 i only had one work out of the box and was only able to repair two of the others the last two didnt even have threads to screw to the battery so had to junk them, obviously no QC what so ever on those ones.
as far as carto tanks they can be great but they also have downsides depending on your juices and how often you like to change flavors i personally like to swap flavors a few times a day and i still do but with different tanks/mods if you only have one carto tank and e-cig you will be stuck with that flavor for a good week until its time to replace the carto,now you can wash them out but its near imposable to get rid of all the flavor from the last juice used so i just dont bother trying to swap flavors with them.
another downside to carto tanks is it can be a tough balance with feeding the right amount of juice depending on a few things including , how many holes in your carto, whether your using mostly VG or PG, how heavily the juice is flavored and how thick the flavoring is,also the temperature of the juice in the tank i tried to use mine last year when i was out shoveling for awhile i just got dry hit after dry hit from the juice thickening up from the cold.
personally i dont think there is a "Best" atomizer system out there tho there are some total junk ones on the market, its all really up to the individual and how they want it to work, some favor convenience,some favor flavor,some favor the "WOW" factor and some just favor "cheep" personally i have tried just about all of them and each one has its pro's and cons so i just make use of what i need at the time, if im going out for a few hours ill take a CE5, if im going out all day ill use a carto tank or vivi nova,if im sitting at home board ill use a drip, but in the end its going to take you time to find what works for you.