I just came home from Europe, flying CDG-SFO on an Air France A388 (A380-800). That was one of the rougher flights I've been on, both in terms of frequency and intensity of rough air. The flight over wasn't as bad, but it was still worse than average in my experience. That's my only memorable experience with anything of that size; I don't remember the air on any 74x flights I've taken (not least because they aren't very recent).
I've never had a bad flight on a Dreamliner or a 777, and have flown trans-Pacific on both. SFO-LHR on a Virgin A340 was also pretty smooth. My long-haul experience on smaller planes is limited, as is my short-haul on bigger equipment; nothing specifically stands out in either case.
None of my experiences should be taken as more than anecdotal.
I've never had a bad flight on a Dreamliner or a 777, and have flown trans-Pacific on both. SFO-LHR on a Virgin A340 was also pretty smooth. My long-haul experience on smaller planes is limited, as is my short-haul on bigger equipment; nothing specifically stands out in either case.
None of my experiences should be taken as more than anecdotal.