Ride quality is something that can't really be measured. To one person the ride might be firm, to another it might be fine!
I have heavily modified cars over many years and with more powerful engines. The first thing I used to do was to firm up the suspension and fit lower profile tyres (i.e. taller wheels and smaller tyre walls). This improves the cornering and steering response slightly and yes, it gives a firmer ride.
But the thing to remember is that if you hit a bump or a pot hole you will get a jolt. Whether that is more or less of a jolt is difficult to tell. But safety in cornering and steering response is perhaps worth it?
As I say, everyone is different. Always remember that going from 17s to 16s is a difference of half an inch of tyre wall (it is the radius that counts, not the diameter. This is very difficult to feel but whatever works best for each of us is what matters.
I really wouldn't drop a wheel size for comfort unless I KNOW that the struts and shock absorbers are in good condition.
They affect the ride quality far more than half an inch of rubber.
I am not saying that people who have dropped in wheel size are wrong, but don't expect a huge difference.
Scientifically, your tyre pressures have far more influence on ride quality, as do the make and type of tyre fitted, so dropping down a tyre size means that you are now running on different tyres and with different tyre pressures and so this often helps with the ride more than the half an inch of tyre wall.
Steve B