It can also depend on the strength of the spring/magnets in the switch.
I have a Vaperz Cloud X1 that had very strong magnets in the switch, which made it hard for me to push the button in, seeing as the tube was so smooth and slipped easily. I swapped them out for weaker magnets that made it far more comfortable to fire...
...but that caused the X1's infamous arcing to get worse, as the circuit was being closed and opened less "snappily".
So it can be mod dependent too. The Dreamer is a lot easier to fire, as is the DJV (even with the smooth sleeve that I often use on it instead of the knurled one).
An AV Able is also very easy to fire.