I've been preferring the Billow V3 and Plus over my Griffins. I get a little less seepage, and wicking is a little simpler on the Billows.
The Griffin looks better (IMO), and the post holes are better. The Billow's positive post holes aren't flat, so it's really easy to cut the leads when tightening down. I always have to tighten very carefully to the point where the wire is secure, but doesn't snap. However, the 510 on the Griffins don't always make a solid connection; I've had them give me "no atomizer" or "atomizer short" a few times on both the Rx200 and Asmodus Minikin.
For filling, I prefer the Griffin, for airflow, I prefer the Billow. The amount of airflow between the two is about the same, and flavor is about the same. However, the airflow on the Billow is quieter than the Griffin.
If there were some way to combine them both, I'd be golden.
BOOM!