Mary,
It's reassuring to hear I'm not the only one who finds the BA more comfortable! It is however interesting that you find the lower back bulge on the NeoAir more comfortable, whereas I think it is the source of my pain. Just another example of why pad selection is such an individual choice.
David,
The new BA has a few differences. First, as I mentioned it feels lest plastic-like and more supple. Perhaps this has more to do with the fact that the new pad uses only 7 air chambers which are slightly larger in diameter, whereas the old BA used 8 smaller chambers. This makes each one rise a little higher, which I suppose gives just a bit more support and 'plush-ness.' It also has a brass breathing nozzle, though I honestly don't remember if my old one was plastic or brass.
When I initially purchased the old BA, I had almost bought a POE insulMat. I chose the BA because the internal I-chamber structure provides a flatter surface. A few years later I bought a POE Ether Thermo6 2/3 to save a few oz. I was surprised to find the larger spacing of the welded-through construction more comfortable; having the larger tubes with space in between really let my hips and shoulder sink into the crevices when side sleeping. But I did miss the I-beam construction, which is more comfortable for back sleeping and keeps the pad a little warmer.
I feel that the newer BA pads provide the perfect compromise between the old BA and the POE; the larger, fewer tubes in the new BA provide the crevasses for my hips and shoulder for side sleeping like the POE pad, but the I-beam construction keeps the pad warmer and more comfortable while on my back like the old BA.
Lastly, the pad just seems to have a little more give to it; it is somehow 'softer' feeling. I can't really describe it beyond that, and my old BA developed a leak and I threw it away (not knowing about BA's repair policy), so I can't directly compare.
One final point; bring a scale to the store (assuming you don't buy online) as these pads can vary pretty widely. I was fortunate to find a long mummy at 22.8oz; my last one was 24.7oz.