I've been using 23c and 25c depending on what's cheap/on-sale. And have noticed only a slight difference - even with the same make/model.
In my limited experience the largest influence on comfort is the flexibility of the tyre. So I guess this is down to the tpi of the casing and 'rubber'. Which may be why Vittoria Diamante's in 23c are more comfortable than Rubino Pro's in 25c.
Surprisingly, the Diamante (despite being a 'race' tyre) has had less punctures than the tough Rubino. And is better in the wet. The only issue is that they cost and wear down more.
So for the past 2 winters, I've been using the Diamante's.
edit: this is on the potholed, broken, gravel strewn and muddy/poop lanes of kent, surrey and sussex.