Personally I am tired of seing all those "revolutionary" improvements in performance, but not much improvements in terms of battery life.
So my vote goes to Better batteries.
I did 8 months of internship at RIM and can say that there is a very specific reason that batteries haven't improved much in the past 5-7 years.
I got the chance to sit through 4 hours of presentations from the battery team seeing how they are tackling the problem. The problem is that we have pretty much reached the limit of what is possible with lithion ion.
There have been successful attempts to use silicon and other inherently non conductive materials in these batteries but they are only squeezing fractions of percents out of it. The capacity chart plateaued years ago and these batteries are ridiculously complex in their design. I wouldn't have believed how much tech goes into those batteries if I didn't see it for myself.
The improvement will come from using less power now, not by increasing the battery capacity per unit of size. Improvements in how the radios and chips conserve power is where they are going with the tech.
Probably the most important points I got out of the presentation that I can actually talk about: Draining the battery almost completely shortens it's lifespan drastically (it's best to charge it whenever you can, I simply charge mine every night regardless of how much or how little power I used during the day), and always use official batteries for your devices. The tech put into those batteries prevents a number of catastrophic reactions that can occur from charging, draining, etc. 3rd party companies cheap out on these protections. Remember; a common smart phone battery, if these protections aren't in place, can explode with the force of a stick of TNT.
I have seen snippets of technology that is being researched at universities including a battery type that uses butane as fuel and has the potential to be charged in seconds with more butane, but last for 5-7 days. So though we have reached the peaks of what we can do with current batteries, there is always research going on for newer, better ideas.