Another vote for unflavored here. Regardless of MTL, DTL, or my setup, I'm unflavored with somewhat different levels of VG/PG depending on the setup.
When I'm feeling REALLY crazy, I'll add in a little menthol concentrate that I made with menthol crystals and PG. Only just enough to be able to taste it though.
Unflavored really isn't unflavored, and I like the way it tastes when the nicotine ages/oxidizes a bit. I mix quite a bit in advance and like it after it's sat a while. I always mix at least a month before I need it. Guess it sounds silly to steep unflavored juice, but it does honestly make a difference.
I get why people like flavors, the best analogy above was the color vs black/white thing. At the same time, I love that I can easily get a month out of a pre-made coil, or only need to rewick my RDAs every two weeks or so.
I also don't have to deal with scrubbing flavored juice out of my gear to get rid of the taste. Some flavors seem to linger on for months. Most of my gear will only ever see unflavored juice. When I try to switch to unflavored in a tank/RDA where I previously used flavored juices, I can taste the old juice for a month easily. So these days, most of my gear is dedicated to unflavored juice. I only rarely use flavors, so I have maybe two toppers that I use flavors with. And I will NOT use flavored juice in any of my squonkers, lol.
Having to keep up with flavors (extra cleaning, maintenance, rewicking) just isn't worth it to me. I honestly prefer unflavored. After all, I vape for the nicotine. And although vaping is MUCH safer than smoking, I wouldn't call it harmless. The fewer ingredients I'm vaping, the better in my opinion.