It’s my opinion you’re discussing three different types of coils (and I can’t tell if that is your intention or not).
“Best” is a moot point, as perception would hinge on the desired result. So I’ll forego that for now and leave that for the individual user to decide.
To clarify (at least my perspective) of the three types mentioned:
Most accomplish this by using two separate wires cut to the same length, and then wrapping them side by side (adjacent to each other) simultaneously.
When a ‘single’ wire is used and folded back alongside itself (to halve the impedance). *Which is something I do [this reduces the time to heat (compared to the similar mass of a fused clapton), while maintaining the doubled surface area.] I use a ‘single’ clapton wire (26/36 SS) to do this.
- is when you have (as mentioned) two or more cores, which are then wrapped together using (typically) a single thinner wire. (EG: 2x26/36)
When comparing the two above examples to one another (performance under actual usage conditions), both have nearly the same mass and surface area, and the impedance is typically within 0.03-0.07 ohms. (When using the same ID, and same number of wraps)
EG: the parallel may ohm out to 0.17-0.19 (depending on leg length), and the Fused (2x26/36) may read 0.20-0.23 ohms.
However, the parallel coil fires (gets up to temp) noticeably faster (on the same mod/atty) in my experience.
Adding flat wire to a coil adds substantially more surface area and mass, so will require ‘either’ more power, or more time to heat the added surface area. The goal here is to increase vapor production (and by some accounts, an increase in flavor*).
*I say ‘some accounts’ above, because it’s my opinion that the atty/mod plays a larger role more often than the simple increase in surface area alone. But it can also be a very true statement (bearing in mind the hardware), so it shouldn’t be immediately nor summarily dismissed when you see such a claim IMO.
At any rate, flat wire is easy to ID visually.
It’s a singular, wide, flat wire.
Fused is three (or more) wires, which can have the appearance of being flat (usually only in the case of a dual-fused), but there are actually three wires minimum.
This makes me think you’re speaking about something altogether different, because there’s really no way to confuse a single solid flat wire with a round one (or even a group of round ones). Much less a group of round ones with a single wide flat one threaded into them.
There’s SO many coil types, much less the creative names (names contrived out of thin air) that accompany, that it’s understandable that someone could get confused about all this. So don’t feel bad if it’s a communication error (whether it’s you or me! lol)
IMO, the only way this could change is if different wire types are used/mixed.
If both coils (regardless of clapton, fused, or parallel) are made of SS, there should be no difference in which one ‘gunks up’ faster at the same impedance, and at the same power/TC and using the same liquid!
If coil materials are mixed (or vary from one coil to another, complex coil or not) then you’re no longer comparing apples to apples. So all bets are off.
Hopefully this helps.
Clarify if need be. Bop me on the noggin if I’m completely missing your question.