I never had much luck with airbeds. I moved over to a normal camp bed in the hope it would be less bulky to carry about, but as it really needs a thin SIM on top, I'm not really saving anything at the end of the day.
I think for bulk, they are all about the same (that's the 3 main sleep systems, SIMs, Airbeds & Campbeds), although camp beds might have a slight advantage.
However, I like my camp bed for 3 main reasons: Firstly; it gets me properly off the ground, which makes it easier to get in & out of & somewhere to sit & put my socks on (although you also get this with a double height airbed). Secondly; you're not reliant on it holding air, I have been "let down" by both airbeds & SIMs in the past. Both can leak, leaving you very uncomfortable, although cheaper ones are more likely to do this. Finally; I get a little storage space underneath my camp bed, which is something you don't get from either of the others. It's only a small thing, but it all helps in a tent.
At the end of the day I think it comes down to personal preference. I would personally like to improve on my camp bed with one of the carp-anglers bad-chairs, but a good one (well, even a crappy one) is quite expensive, they are bulky but there's no need for a SIM on top. But i may get one & decide I don't like it. My camp bed cost me nothing, it was hanging around in my parents' loft, but would've only cost about a tenner anyway. I haven't actually got a cheap SIM for it yet, I just put an old sleeping bag on top & sleep inside a kingsize winter duvet, which is folded in half.
Night night, everybody
when space is an issue, just take a pillow-case and stuff it with your clothes. We usually have our feather 'duvet' jackets, which make excellent pillows 
