I enjoy the simplicity and elegance of a mech. No frills and no gimmicky nonsense. I know what I want and how to get it. I have simple needs. Even something as basic as a Sig 150w TC is more than I find I really need for my drippers. I'd rather have something something smaller and more rugged. Honestly, dialing in the wattage is just extra hassle for me.
I learned to build on mechs, so for me, it's much more intuitive to build to mass and power level at 'natural' voltage. I can build for a mech and have a pretty good idea of how it's going to perform. They work the way I want them to with no need for adjustments. I have a wide range of different builds for different devices mapped out in my head.
The way mechs hit is unique, too. I like to think of it as natural temperature control. The initial peak is enough to get the coils up to the desired temperature, by which point the voltage is going down, thus maintaining more of a steady plateau, whereas a regulated mod delivers consistent wattage that drives the temperature ever higher at an increasing rate. Mechs offer a more balanced heating curve - they plateau. It's really difficult to describe why, but I prefer the way mechs hit and a lot of it has to do with that power roll-off. I find it easier to take deeper hits, even with very hot builds.
I personally think that everyone should, when they're ready, pick up a mech and learn to build for one. It really has a way of expanding your understanding of what makes coils perform in certain ways. It teaches you to be more deliberate with your builds and makes the whole process of coming up with and trying coils a lot more challenging and enjoyable. It's a good exercise for experienced vapers. What you learn while building for mechs carries over to other types of mods.
I especially love a good unregulated series vape. The extra voltage lets you build massive coils with finer gauges, which I find brings out a lot more nuance in flavor than you can get from those super-low-end sub-ohm builds. I like the heating properties of the finer gauges, too. Though they're still big coils, there's still less mass, so they can be made to deliver a very hot vape that never overheats. They gain heat faster with less current and also lose heat just as quickly. Building for series is tricky at first, but once you understand a few fundamental things, you realize that it makes controlling heat much, much easier... ...especially for your high-surface-area builds.
Series also gives you kick-ass battery life. You can run a .4 for ~160w and only draw 20A. A more reasonable .65 gives you about 100w for 12A. So it's comparable to running a series regulated mod... ...sometimes even better because a mod with no circuitry is more power-efficient, whereas a regulated mod will sacrifice some power just to run the buck converter.