I mostly commute and own three 700c road bikes in my "stable". My 1984 Nishiki International, a 2006 Felt F-65, and a 2015 Charge Plug. The steel Nishiki with its thin seat and chain stays and tapering, rim brake front fork The Nishiki has lovely, comfortable frame flex, but was a little harsh with the original 23mm tires that it had when I acquired it in 2009. Rattled a bit with the 23s and still with 25s. At some point I put 700x28s on it and even at 90psi it now rides like a dream, At 75psi, it's really sweet, but a little too mushy. (I tried 32s but they would rub the fork crown)

A year and a half ago I bought a 2006 Felt F-65, which has an aluminum frame and bars, but carbon-fiber seat and chain stays, thisk, stubby fork, seat post and cranks. 700x25 seems to be the max tire size. I also fill the tires to 90psi. The whole set-up has noticeably compliant ride, but not as much as, and different from the Nishiki. The Nishiki feels "flexi", the Felt feels "smooshy", but not in a bad way. Kinda like it has bushings vs springs.

My main commuter is a steel 2015 Charge Plug but stouter (and heavier) than the NIshiki. The Plug has a thicker, disc brake front fork, and thicker chain and seat stays. Very, little flex, but there is a hint. I run the 700x38 tires at 90psi. With its rack and fenders, the bike tend to rattle slightly on rough pavement and over bumps. With its longer wheelbase and more relaxed geometry, the ride motions are slower than the two other bikes. It's comfortable, but is missing the extra comforting flex of the other bikes. Lowering the psi in the tires does nothing to soften the ride. But the Charge Plug is a fast, comfortable cruiser, especially because of the slower ride movements.

My old commuter is a stiff-framed 1997 Nishiki Blazer, and fatter 26x2.125 tires make all the difference in comfort...with racksm fenders and folding baskets, it rattles.

My 2007 20" Dahon Boardwarlk folder (steel) has some frame flex, but, kinda lateral, not the good kind. The long aluminum seat post provides some flex, but it's a little weird. With bull bars and 20x1.75 Schwalbe Marathon Racers it's comfortable, but slightly bizarre.

My 16" Dahon Getaway (steel) project bike is a rickety mess and not really comfortable. But it is the old frame design and folds really small. It serves a purpose, and I have been updating the gearing and brakes for speed and safety. But it will never not be rickety.

I might also add that all my bikes have padded seats, and padded Bars, but not as much as before.