I used to find the ride on 19" RFT winter tires was less harsh but I couldn't wait to get 20" RFT summer tires back on the car. The 20" tires did seem to improve the handling (e.g. entering and exiting off-ramps as I think rh71 has commented on before).

Appearance and the general handling feel is why I've gone to 20" tires for both my summer and winter tire sets. Most of my winter driving is with very little snow or ice so handling is important to me.