Fluid is quiet. Resistance is exponential, increases kind of quickly. Your gearing and cadence make the change in resistance. As I only have fluid trainers I'm kind of stuck on one. I've been struggling in the small ring, big cogs for a couple weeks now.

Magnetic is noisier but still not bad. Resistance increases linearly, i.e. not that quick. I prefer this when I'm not fit as it's easier to make small adjustments in resistance, i.e. the bike's gearing is your minor range (at level 1 it's pretty easy regardless of gear), the magnetic one is a major range (difference between 1 and 7 is "big").

If I had a mag trainer now I'd be at level 1-2 and using whatever low wear gear (big ring, middle cog).

When I'm fit the fluid trainer is good, I can hammer the big ring for a while.

To isolate noise from downstairs you need to have air or huge mass in the floor. So concrete floor (think Las Vegas strip hotels - you can't hear through the floor) or air filled something between trainer and floor. The exercise mats help (they have little air bubbles). A long time ago someone suggested theoretically using a lot of inner tube inflated under a big piece of plywood. The plywood would make noise but the innertubes under it would isolate the noise from the floor.

If doing fluid, get the KK. I've had two Cycleops leak on me, working on the third.