If your looking into a kanger, I would bet a mini plus and nano plus will come out come out before before too long.
I have a billow, really like it, decently easy to wick so it doesn't leak while upright, harder to wick to not leak while on it's on it's side, but is possible. Bottom filling is a pain, I've went to top filling by unscrewing the top, I'm about 50/50 on flooding the deck and not flooding it. Unless you spend 5 minutes slowly bottom filling, you're gonna back up in the screw fill and waste juice anyhow. I don't have that patience, takes 30 seconds to top fill and may flood.
I'm not a rba expert, have a kayfun 3.1, orchid and fogger, the billow is the only one I still use.
I was really eyeing the goblin, as it looks great, hearing good things, and was getting fed up with billow side leaking and filling. Once I got the kinks worked out I'm a bit more content. What has really caught my eye is the cthulhu, it looks about the same as the goblin with some minor upgrades, but probably the most substantial is the top fill feature. It is new, so it is probably hard to find.
Probably the biggest thing is whether you want single or double coil. Seems that a lemo or subtank are the go to for single coils and billow or goblin for double coils. .... although they are newer the goliath and cthulhu look good (especially the cthulhu).