guy aitchison had some good words on this subject:
Pneumatic and electric rotary machines are another animal entirely. What I'm focused on here is what I refer to as a "stroke profile", where you imagine a graph of the actual motion of the needle as time passes. With a coil tattoo machine, you'll most likely find that the needle pauses for a period of time at the top of each stroke as electromagnetism builds, then when the magnetic power is adequate to overcome the spring tension, it suddenly pulls it down. As the armature bar approaches the coil, its distance decreases, hence greater magnetic pull as it moves downward... so in effect, the needle pauses at the top, accelerates toward the skin, then pulls out immediately without any kind of turnaround time. With any rotary tattoo machine, the opposite happens- the needle is always in motion in a smooth oscillating motion, meaning that the needle is actually slowing down as it approaches the skin... it slows down to a stop, then speeds up again gradually as it pulls out. In some ways, the needle strike of a rotary tattoo machine is the polar opposite of that of a coil tattoo machine. What this translates to is that with rotaries, the points spend more time in the skin, so the tattooist needs to adapt their hand motion to this or there is a continual sense of the needles snagging the skin. Many color realists have found that this modified hand motion lends itself to their working style perfectly, although I find that it cramps the style of my rapid hand movements, which I like to keep uninhibited."
in the end, whatever works best for you is best for you!