I have the Arctic, the Atlantis, Subtank Mini, and Subtank Nano. I've never tried the Delta.
The Subtanks have it for the flavor department. If you vape complicated juices the Subtanks will give you all those nuances you'd expect from a nice
rda at conservative wattages. I think it has to do with the way the Atlantis and Arctic channels the airflow
through the center of the coil vs the Subtanks that channel it
around the coil. Likely making more air actually contact the coils. Rebuildable deck is included with the Mini and fullsize but I rarely use it as it performs no better than the prebuilt heads plus those can be rebuilt quite easily themselves. I'd almost say the prebuilts wick slightly better as I can often notch the Sigelei past 30 watts on them but get punished quickly if I attempt to on the RTA deck.
The Atlantis is a slightly more airy draw than the Subtanks but seems to absorb an extra 5-10 watts without dry hits. Good flavor only barely muted vs the Subtank but leaning to larger clouds due to that slight airflow increase. Rebuilding these is a total PITA in comparison but can be done carefully. Just buy the heads to avoid frustration. An upside is the recent availability of a longer tank to increase capacity. That's just a win/win in the portability dept. especially if you already have an Atlantis.
The Arctic is more of an Atlantis on steroids. Very similar head design just with
huge wicking holes allowing 2-3X the wattage. Still have yet to hit it dry. Honestly the vapor's temperature will make you turn it back down long before dry hits will. Saturate an Atlantis head then hit it once quickly @ 70 watts and you'll experience what the Arctic can offer. For once, the hype is well earned. There are some cons though: First, 3ml capacity is laughable with how fast 100 watts can guzzle your liquid. An upgraded tank will be a sure thing but may not become available for a bit. Second, this thing almost has too much hype around it so it's hard to get your hands on one and it's replacement heads. Of course Horizon will ramp up production on these and this problem will most likely solve itself. Third, I haven't attempted it yet but it would appear that rebuilding these heads would likely be as difficult as rebuilding the Atlantis heads. Small knock: I wish it had even more airflow to match it's ridiculous ability to soak up the watts.
The Freemax Starr, High Voltage, and a couple others I can't remember the names of right now are very close in design and performance to the Arctic and also are very hard to keep in stock. I went with the Arctic though as it's the one with all the hype. Not that it will perform any better for it but the one with hype = the one everyone will buy = the one that will enjoy a longer support life with replacement heads, tanks, accessories etc. due to a larger installed base. With it's excellent performance and ability to never hit dry it has replaced my Subtank as my go to but not quite retired it. There's still flavor nuances that I can only pick up with the Subtank or an RDA.