I own all 3. This is my impression of them.
Aspire Nautilus... For me this is by far the best retail non-subohm clearo. It has great flavor and can produce a ton of vapor. I would prefer a bit more adjustable airflow than it's 4 options, but wide open it has the best airflow. Direct lung hits are possible. In my experience, it works best at 15W-19W power ranges and thanks to it's large wicking holes and cotton wicks it works well with 50/50 or 60/40 VG/PG juice mixes.
iClear 30S... My wife uses this religiously. I think it actually has the best flavor of these tanks, but it has a very tight, non-adjustable airflow. Works fine if you just do mouth to lung hits and want a tight airflow, but it also tends to give dry hits and burns the juice at anything over 9 watts because it's so restricted. Stay in the 7-9W range and it works fine though. Technically it's a top coil tank so you would want to use it with thinner juices. 30/70 VG/PG works well, 40/60 VG/PG is right on the edge of it's limits. It also has a plastic tank which can fog up, scale, or crack with certain juices. Avoid citrus or cinnamon juices, it will mess the tank up.
Kanger Aerotank... This is probably the most disappointing tank for me. It has the best airflow adjustment, but is still very limited on it's overall airflow. This is for mouth to lung hitters only. This tank also has the least flavor. Flavors are VERY muted with the Aerotank, to the point where some of mine have virtually no taste at all. It also has small wicking holes so it doesn't work well with thicker juices. I personally wouldn't recommend going lower than a 40/60 VG/PG mix with the Kanger heads, unless you really like dry hits. In my experience this tank works best in the 9-12W range. Any higher than 12W and it starts tasting burnt and giving dry hits due to the restricted wicking and limited airflow.
*** NOTE: My impressions are based on the full sized Nautilus, not the Mini which based on reports here seems to be very problematic for some. The full sized Nautilus works great and I've not had one single problem with leaking, gurgling, or spitting.