I agree on the seat width being important (I'm both overweight and tall) - this is why I avoid exit seats on the "nicer" airlines (since that usually means the tables/screens are stored/flipped-out from the armrest --> narrower seats) - but on budget airlines this is usually not the case. (at least in the EU/Middle East region)

But the nicer airlines offer general legroom's that's survivable - some budget airlines my knee is basically in somebody else's back (thinner seats help here).