looking out over the next 12-18 months, which processor is the best balance of performance, low heat, and battery life for the next generation of Airs?
it sounds like a lot of people are hoping Apple doesn't go with SandyBridge, so is the only realistic alternatives sticking with C2D or AMD? And is AMD a definitively better choice than SandyBridge?
Sandy Bridge is definitely the best for that but Apple would have to use the Intel IGP which isn't exactly great. It is a huge step over the old Intel IGP but it's still worse than 320M (especially LV and ULV chips' IGP). However, according to the early tests, it provides great CPU and battery performance. As you said 12-18 months, Ivy Bridge will likely be out already but giving so faraway timeframe makes predicting very hard because we have absolutely no idea what will be the best chip then.
Currently AMD can't offer anything competitive. Llano looks the most promising but it was pushed to Q3 2011 and even then it will only be few desktop chips. It was supposed to come out in Q1. The issue with AMD seems to be that they can't stick with their schedules, the same issue IBM had with PPC which was one of the main reasons why Apple switched to Intel. AMD would only offer good graphics compared to the Intel IGP but Intel should still be ahead in CPU performance, especially as Ivy Bridge will be out soon after Llano.
Core 2 Duo is still plausible as Intel will be shipping them until Oct 20, 2011. I would, however, expect Apple to stop kicking the dead horse and move to newer CPUs.
I heard something about a squabble between nvidia and intel. The CPU and GPU on MBA have to be almost glued together and there is some IP hassle.
So if the IP hassle is NOT resolved and if these two providers are selected for the next MBA, I doubt there will be anything exciting to look forwards to.
It has been solved, NVidia is not making chipsets anymore.
IMO Sandy Bridge is the only viable option at the moment. NVidia ain't making chipsets anymore so C2D and NVidia IGP can be ruled out. AMD is too risky and likely not ready before the next update. This leaves us with Sandy Bridge.
Of course, we could talk about ARM, especially as NVidia will be making ARM based CPUs in the future and they said we will see them in all kinds of computers including normal laptops, tablets, desktops, even servers.