I agree on you having a poor battery for mechs. With regulated devices, any old 20A cell will do. But mechs have no safety nets and they like high-current builds, so only the best 20A or 30A cells will do. They don't even cost more to get. Take the advice given and get either sony VTC4's or Samsung 25r's... ...preferably VTC4's if you want to do fast, high-mass builds. VTC4's can be had from
illumn.com for $6 a peice.
LG HB6's are arguably the best in terms of voltage and really the only true 30A cells worth talking about. But the 1500mah capacity can be hard to get past. The runtime on them is ridiculously short, though the performance for that short time is as good as it gets. VTC3's are similar in that regard.
Low sub-ohming is the way to go for speed on a mech, but it's important to do it the right way. The battery is the most important thing to not be lazy and skimp out on. Not just for safety, but because voltage drop is a big deal with unregulated power. An inferior quality battery outputs less power under load, meaning a slower vape. It's also a sign of the battery being more strained.
If it's in and out, then it could be a button or contact issue. Make sure everything is clean and check out the button to make sure it's throwing down evenly every time. You may have to change the way you press it to make it come down right every time. It may be the mod.
Once you get all of that worked-out, I say shoot for a .18-.24 with that dual 24... ...it just has to be a little smaller: 5 or 6 wraps around a 2.5mm. The vapor and flavor will still be there, but it'll be much warmer and faster. On tube mods, there comes a point with the mass/power ratio of the coil where it's too big to be powered optimally, meaning that if you make the coils too big, you won't be able to take advantage of the surface area because it's not getting adequate heat pushed out. Smaller is often better with tubes... ...for speed, flavor and vapor.
Those were my personal favorites starting off. But again, if you're gonna do a .18, 30A batteries are not optional. The .24 is perfectly okay with 20A cells and performs great.
For speed, 28g is handy in the .28-.32 range. 6 or 7-wrap, 2mm dual parallel 28's produce a lot of flavor and vapor really quickly. They're little coils that pack a nice punch. Faster than dual 24's even. You can also try twisting them instead if the parallel is too difficult, but it will alter the texture. Some like it, some prefer parallel.
If you can do the dual-parallel 28, then you'll love the triple. Lotsa clouds and flavor for that. Perhaps more than a dual 24g. Faster, but also hotter. Maybe 6 wraps @ 2.5mm. Should be around .18.
I dunno, these are really just my preference. There are always compromises.
@Zamazam mentioned SS. Personally, I'm not a fan of it, but it is very snappy. Another option is nichrome, though some people claim it has a funky taste. I haven't experienced any difference in flavor and it has lower resistance for it's mass/thickness, meaning a nichrome coil of given size will pull more power than a kanthal coil of the same size.