Also depends on the sidewall, whether it is SL or XL, and it's total load rating. An XL sidewall tends to ride stiffer, though not necessarily in a bad way.
Lighter aftermarket wheels can help with the ride quality, as they can be slightly more compliant (vs OEM cast-aluminum clunkers) not to mention, the suspension can control them better due to being so much lighter.
As I mentioned in my post, the ride is a little-bit stiffer over potholes (Having moved from a SL touring 222/55R17 to an XL Performance AS 235/50ZR17) But, on smooth or cracked pavement, I think the ride quality has improved dramatically. (Thanks to the flow-formed wheels as well, i think.)
With that being said, my idea of ride comfort is based more on feeling connected to the road, good road feel, controlled, responsive body movement over outright suppleness over bumps. Mazda's are not comfort cars, no matter what tires you put on them.
If you need softer ride, you should ditch the 19's all together and go 17's or 18's.