I would love one of these, but would need to adjust my method of building and vaping.
I've gotten used to big and low builds and on the RX i surpass 60w more often than not.
A single battery mod would force me to build higher to get any decent flavour and battery life out of it, in that...
My vote goes for the velocity.
Easy to build on, for when you start your standard builds, but as you experiment with thicker gauges and exotic coils, you'll have enough space to build in, and more than ample airflow.