I have the Subtank mini, the Delta 2 and the Arctic. I also upgraded from a Nautilus and I also prefer lung inhales
Out of the 3 I prefer the Delta 2. If you're into building your own coils unfortunately you'll have to shell out an extra 10 to 15 bucks for the RBA deck but in my opinion if you're gonna rebuild the Delta 2 is the best option of the 3. It likes higher watts and provides more flavor in my opinion. The Subtank mini is a good tank to build on but I've experienced more leaking and less flavor. I'm a novice builder though so the leaking might be my own issue. I like the higher watts, the flavor and the fact that there's less glass exposed on the Delta 2. It is a bit difficult to fill depending on the bottle you have. The needle nose squeeze bottles like Vape Wild uses are no problem. Some wider tipped dropper bottles I have are a little more tricky. Nothing major though. You don't have the clearlest view of how much juice you have left but the benefit of that is a tank that's more metal than glass. On an iStick 50w I use the Delta 2 around 40w and the Subtank mini.
The Delta 2 is my suggest if you'll primarily be using pre built coils. The Arctic is a very close second. As a matter of fact if you're a big user of pre built coils I'd say you can't lose with either the Delta 2 or the Arctic. I've found that the Delta 2 pre made coils are usually more expensive (for a 5 pack) than the Arctic but then again I haven't bought Delta 2 coils in a while and recently found a great sale for the Arctic coils.
As far as I know The Arctic doesn't have the option of building on. It is a great tank with the pre built coils. I use the 0.5 ohm coil at around 42w and the flavor is outstanding. Very airy draw but it can be adjusted. It does drink juice quite a bit.
I wouldn't recommend Subtank mini if you're using the stock pre built coils. I have the 0.5 ohm coils and I find it doesn't perform well above 30-35w. Some dry hits and a burned taste. I find the flavor muted on the Subtank mini with the stock coils. I've built on it and you can crank up the watts a bit. I use it around 40. The flavor improved but I still find more flavor from the Arctic and the Delta 2 regardless of what coil is in it (pre built or built by me).
I'm a noob at building so take my review with a grain of salt. A lot of people love building on the Subtank mini and it does come with the RBA deck so that's a plus. I prefer higher watts and I still use a pre built coil often. If that sounds like you then I'd suggest the Delta 2 or the Arctic. Good luck.
TLDR - if building coils is a must avoid the Arctic. I prefer the Delta 2 to the Subtank mini. Probably can't go wrong with either. If relying solely on pre made coils I'd avoid the Subtank and give a slight edge to the Delta 2 over the Arctic.