Eh, dunno.
I used a bunch of mech mods for the longest time, but once high-powered regulated mods became more easily accessible I totally ditched them. I don't really know why people continue to use them other than aesthetics. And aesthetically, I'll admit, a mech mod feels great in the hand. If you've got one with a nice firing button, it can really be a pleasure to pull on.
It bugs me when people say they use mech mods because, "THEY HIT SO MUCH HARDER BRO". That's just flat-out not true. If you put the same atomizer on a regulated mod, set to 4.2V, and a mech mod with a fully charged battery, they SHOULD output the EXACT same amount of vapor. However, because of voltage drop/nominal battery voltage dropping with use of the battery, this is never really the case. The same build that chucks at 4.2V on a regulated mod kinda just fizzles on my mech mod. It's not entirely unvapeable, but it's not the same experience.
I use regulated mods for consistency's sake, primarily, along with the ability to build a larger range of coil resistances while still maintaining a similar, pleasurable, experience -- which also related to consistency. I'm not one to rebuild every week -- hell, my .6 ohm Doge build has been in there for what.. 8 months now? I don't know, its been a whiiile.
But yeah, it's definitely a matter of preference, but don't let anyone tell you that you should use a mech mod because it "hits harder".
Also, generally, regulated mods are prohibited in cloud competitions. Personally that's not of concern for me, since I think cloud competitions are hilariously silly, but whatever. If that's important to you, that's a reason to use mech mods.