Top coil works for some folks, while others like the bottom coil designs better. There are pros and cons to both, and it definitely has a lot to do with the juice you're using. I had very little luck with bottom coil cartos for some reason, I blame my fondness for VG and my chain vaping habits. The Fluxos have been my "I can vape anything on these" carts for a while now - I always keep some on hand just in case whatever shiny new thing I try doesn't work out. Yeah, they have their quirks, the occasional mouthful of juice If it's been rolling around in my bag, or if the cat knocks it off my desk - but it's easy to clean, burn and good to go (and they're fairly cheap so if one dies, just whip out a new one).
I do love the concept of bottom coil designs because they don't leak, and you do seem to get more "juice" enjoyment out of them - but again it all depends on what you're vaping.