I've tried a bunch, kept the best, and use the top 3 or 4 to switch flavors - I only have one Kayfun (which gets my favorite juice of the moment), and I'm constantly changing juices, so I keep the clearos around to rotate through. I'm a flavor guy, so for me, flavor is a higher priority than vapor. And tastes are subjective, YMMV. That said, here are my preferences on the clearos I'm using regularly. Just to be clear, all of these are excellent and in a class of their own. The differences I'm talking about here are small.
1) TIE - Kanger ProTank 3 with air control base (which is sold separately) and Kanger Mini ProTank 3 - These are the ones where the flavor comes closest to my Kayfun. Good vapor production and excellent flavor. Replacement heads are cheap, last a while, and I haven't had many that are DOA. I only tend to keep one or the other of these with me, but my second favorite flavor goes here.
2) Aspire Nautilus - Great vapor production, and excellent flavor at first, but the attys die more quickly than the protanks, cost more, and I've had about a 30% "crappy out of the box" ratio. With a fresh atty that works well, the Nautilus is slightly better than the protanks, but it's good for a day or two, then drops quickly. I usually keep one juice around that's a step higher in nic than the rest, and this clearo has a good throat hit if you use the tighter draw, so I usually keep the higher nic in here for when I want or need something that hits harder.
3) Kanger Aerotank - Very good flavor and vapor production, and the airflow control is included instead of being a separate purchase. That said, the flavor is not quite as clear as the tanks above. This one gets the juice I'm going to use the least out of the four.
I also keep an Elego BCC Mega in the drawer in my desk at work in case of emergency. I'm pretty sure this is the same as the SmokTech, and it gets the job done, but it's not on the same level as the ones above, so it's a backup.