24fps or 30fps slowed down

Back in film movie days, they weren't trying to be "cinematic" ... they were trying to match the way the eye "saw" movemement more naturally. To get the right, more naturally appearing blur, on movement.

So shutter speed at film speed is actually the main part of most concepts of "cinematic" ... as what we're used to was pretty tight to 24fps, with a "180 degree shutter" ... in other words, shutter was open for half the fps, or ... 1/48th second.

It's the combination of that fps and that shutter speed that supposedly more matches the way the eye sees movement. I've seen comments that say at 29.97, using X shutter speed gets closest to matching 24/48.

With digital images, that really should be the goal, but we've got another problem ... most film movie cameras had a "global" shutter, that exposed the whole frame at the same instant. Most digitals use a "traveling curtain" or slit shutter, that starts at the top or bottom and crosses the sensor.

So movement of the camera in pans or whatnot, can cause "rolling" of the image, where maybe the top or bottom is moving a little different than the other. Or "judder" or "jelly", whatever you want to call it. If the shutter is open more and moves faster, the less rolling/judder you see. 

For cameras (as in most DSLRs) with a notable rolling shutter, very slow movement of the camera is a priority.

Those are things that can be as or more important than what fps was used. It's all part of making the movement visually ... natural. The right amount of the right type of blur.

And I would normally prefer 24fps @ 1/48th sec, slightly. Though depending on the camera shutter and movement, some things might look a bit better at your other option. So ... as in all questions of this nature, test it.

Then you'll know which you prefer. And that's what matters, really.

Neil