The  FLD's are both air ride.  One does not have an air ride cab, it's mate does, same year, we bought them within a month of each other, came from same fleet, miles within about 100,000, we pretty well always used the air cab unless we're using both or there is some reason it's not availible.  I'd have to look it up but I'd bet we've put three times as many miles on the air ride cab.  The one without it has the dash trying to fall on the floor, one with is still tight.  They were both tight when we got them, have put maybe 50,000 miles on the one and 150,000 on the other.  Both are second string now, but were the "good" trucks for about seven years. 

Our Volvo is 4 spring.  Cab is suspended but it's springs rather then air, but works pretty well.  Short wb and not a good ride when empty, not bad full.  The steel cab seems a lot more solidly built.   Our first LT9000 was spring ride with no cab suspention at all and about the same wb...the Volvo definately rides better then it.