Both work.
For sub-ohm vapers, building coils 0.8 or less, the mech mod will suit you better.
For builds 1.8 or greater, you'll get more out of the regulated mods like the DNA 30's.
For example, a 0.5 ohm coil at 30watts would run 3.87v. A 2.0ohm coul at 30watts would run 7.74v. Using the 0.5 coil with a fresh battery would run you 4.2v. That would actually be 35watts.