I'd actually go one step beyond this and go fleet + class atmosphere...
Not quite in the
issue, but actual air quality. One flight to SFO on the BA285 (Worldwide fleet, 747) I was in World Traveller. Cheerfully plonked in 52B (the poor mans 64A...). But with the iPads showing me as a GCH, one of the crew continued to treat me to rounds of impromptu G&Ts throughout the flight. 40 minutes out, he then insisted I move further forward given the queues at immigration at SFO. I quite enjoy the port-side views of San Francisco so kindly declined until he suggested First! 5A!
So 20 minutes-to-landing and he grabs my bag (!!) and marches me up from one end of the plane to the other (can't think what other travellers thought...). Tying back to the thread, one of the things that struck me at the tail end of an 11-hour haul to California is how much fresher and moist the cabin in First felt in contrast to all the other cabins (having walked through the entire plan!). Perhaps it's the effect of fewer people? Air fresheners? Flowers? (I wouldn't know if they've come back).
I'd still agree with the consensus that 787 > A380 > 747 > ... > 777, but also pose a question F > JWY.