Normal descent rates will vary by operator and by airframe, but in general they follow this logic:
- Power at flight idle,
- Airspeed at or near max mach number or max KIAS,
- Spoilers stowed.
Generally they wont push airspeed right up to the limits and incorporate a small margin, but this is general idea. This is the most efficient descent because it means you stayed as high as long as possible but not so long you need to "cheat" with lift-destroying devices. Whatever descent rate this configuration results in is the "normal" rate.
The actual descent rate will vary in practice. ATC might descend you early, and then you will use a lower descent rate to stay higher longer (500 fpm unless they ask for more). If they keep you high too long, you opt for a higher rate of descent (spoilers!). The descent rate chosen will also be effected by the vertical wind profile. You may have a strong headwind and since you are covering ground slower opt for a slower descent, but if that headwind reduces in strength that might end up biting you later. Many descents are "at pilot discretion", and thus we'll typically stay high as long as we can until we can descend at (or near) idle to meet our crossing restrictions.
Passenger comfort isn't directly correlated to descent rate. Many pax will claim their ears popped more, but in reality the cabin pressure change is the same regardless of the descent rate. Things the pax are sensitive to that do occur are accelerations, and how fast the airplane is pitched into the descent will have a large impact on how the descent rate is perceived in the cabin (This is the same reason a vertical deviation of 50 feet in turbulence makes passengers think they dropped 1000 ft, it is all in the acceleration). Deck angle may also play a role in passenger perception.