I'am thinking about getting an air bed  which one. is best to buy ?

I can only tell you that we've heard almost no good reports on air beds here.
I will tell you though, that I have an acquaintance who bought Select Comfort - the higher end one - and loves it and he bought one for his parents and they love it.
I just find them overpriced which is why I never tried one.
Don't be surprised if you don't get much response here on this question - I just don't think many here have experience with them.
Good luck!

thank you

What a lot of people don't know about FlowBeds is that they are a very diverse mattress company. They principally deal in latex mattresses. But they also have waterbeds, and what looks like to me to be, a hybrid latex and air mattress. Possibly they sell a purer air bed mattress, I just do not know.

Here is a link to the highbred I mention .  http://www.flobeds.com/air/index.htm

But I would recommend calling them and talking to them about what they do offer in air beds.

There ARE excellent air beds out there if you only look. I suggest "building" your own. I just posted many posts about my own experiences with several mattress and I am back on air. I'm on my way to bed but I will send you some links in the morning. Forget the "Sleep Number" beds. pure bunk. You have to be willing to build your own. I sleep on a queen size Areo bed (top of the line, $250) inserted into a zip around mattress cover, a 2 inch latex topper in there as well which really makes it special. You can go fancy, add wool, memory foam, you think it you can build it yourself, way cheaper. Even Overstock has just as good as Flobeds stuff.

Alice in Wonderland

I could see air being viable with the right upholstery over the air chambers.  but basically air behaves exactly like a fluid when it is in an enclosed space, it takes the path of least resistance, which from a support standpoint usually isn't good.  Too little PSI and there is virtually no support as the air simply pushes out on the sides of the chambers moving away from your body.  Too much PSI and you will simply have too much pressure for even the heavier parts of your body to overcome and sink into the chambers properly.  Unfortunately the sweet spot between too much and too little air pressure is theoretically very small.  There are some air beds that are completely self adjusting like the SAT bed that Christopher Reeves (RIP) was using before his death.  I always thought that in principle a self adjusting type of air mattress would probably provide a much better overall ergonomic feel than something like a Sleep Number bed where you are adjusting the PSI level equally for each chamber on your side of the bed. 

I do lack personal experience with them myself, and I even have access to some good quality air mattresses from one of my suppliers but because they are not a self adjusting system I so far have stayed away, and it was pretty hard to justify the cost being close to something like a Sleep Number in terms of pricing.

Which is exactly why you need to enclose the bed like a waterbed, lining the whole thing with baffles on the side, you should see the new ones, they are made of rubber and slope, holding the sides steady. I find the stuff you write so very interesting! I thank you once again for the really good info.