Actually... one is not more or less efficient than the other. For every Ohm's law derived wattage, there will be an "optimal" build... or at least as optimal as you can get for your preferences, juice and equipment.
You set your desired goals, like... for a single coil build at 0.4Ω...
"I prefer as my number one desired value, a 300 HF +/- 20 mW/mm²"
From this, you work out what wire gauge you need to obtain the above, with secondary values of:
- Greatest surface area.
- Lowest HC (time to temp).
- Least leg loss.
If you can't get all the values you want, then maybe you just get as close as you can... and maybe accept a kinda slow HC to get great numbers everywhere else.
Maybe you need to adjust your net resistance up or down, or try a dual parallel build with all new variables, including a different RDA.
At some point, with enough experimentation you find the best combination of variables for every atomizer you own. That experimentation time can be reduced dramatically if you have a good understanding of SE... and what the variables are that produce a vape you like.
Hell... your build can be available wattage dependent, juice blend dependent.... or maybe you like
really short draws off a 550 mW/mm² build.