imo neither, both tanks have been out on the market for quite a while, there are better/easier to build RTAs out currently that you can look at as well.
I have the Billow V2 Nano, just purchased a billow v3...the billow v2 is a great RTA, awesome flavor, clouds all day, however, no top fill, 4 post rebuildable base, harder to build than a velocity style, no top fill, none of the bells and whistles of top airflow, juice flow control, etc etc...
Its a nice tank to include in your collection, but if you're looking for an all day beater, I would look at newer tanks out there.