I usually get a lot of life out of cartos filled with unsweetened Almond Horn. At a 80/20 mix that one starts out so sweet to me that I have no desire to experiment with adding more. Don't get me wrong, I love the sweetness of it, sometimes that's what I'm craving, but you can have too much of a good thing.
My custom (unsweetened) blend of orange/clove/cinn lasts even longer than AH, usually. I think the times its cartos die faster is due to the cart, not the juice. This is my go-to when I dont want sweetness at all. It's potent, you get a lot of sensation from those three flavors, so if I'm cranky it's a good choice because it feels the most like smoke to me. Even though it's been two years since I had a cigarette I still find myself needing a close approximation to it in feel, at times.
My other repeat bulk purchase, can't live without it custom is unsweetened choc/peppermint. No cookie, no sugar, just those two flavors. This is slightly sweet on it's own, which works really well for me. The idea was to emulate an after-dinner mint type of thing, but whether I've just eaten or not this one is almost always palatable to me. It strikes a balance between my other two main flavors and, as a result, gets used more than either of them. Added bonus, the peppermint not only adds a little sensation it freshens your breath. Awesome, right? It's lifetime is a probably slightly less than the clove, but a notch above AH.
To tell the truth, the only unsweetened flavor that really sticks out in my mind as being a quick killer is AC. I've discovered that adding sweetener to my choc/peppermint makes useful carto life plummet. Most sweetened liquids seem to wipe out my carto performance after running only 3-5Ml through them.
My initial experience with sweetened POB (I'm halfway through my first bottle) is that it's not as hard on things as the other sweetened juices I've tried. It still causes earlier flavor drop than unsweetened flavors, but not nearly as fast as any other sweetened things I've tried.
If you stay away from super-duty cinnamon and sweetener you should have pretty decent life expectancy from most flavors.
