Most Keynote versus PowerPoint evaluations on the web count the number of features, slide transition effects, or the quality of the built-in themes. So this is maybe the explanation why these features get some much prominence in marketing of both products. Personally, I find them the least important aspects of the software. What matters is how easy your workflow is: manipulating objects, changing the order of slides, managing images, creating and editing data charts. My review will focus more on these issues.
People say that the best Apple products are those that Steve Jobs used frequently personally, and Keynote is such a product, and it shows. The interface is lighter, fresher, simpler without PowerPoint’s baggage of older versions.
The concept of the inspector window with the properties of any object you click at (image, shape, graph, text) is incredibly useful and time saving compared to looking for the right menu in PowerPoint.
One of the biggest pains of PowerPoint 2011 are the drawing guides that you cannot lock. Re-size an object near the blue drawing guide, and tsjak, off she goes. Not so in Keynote. Aligning, positioning is all easier and cleaner.
With PowerPont I found it easier to customize my toolbars though. Centering, distributing, aligning multiple object requires going into a menu and clicking an option. And these are functions that you need to use all the time.
The concept of masking images with a shape is also a refreshing idea in Keynote instead of cropping in PowerPoint. Still, you need to get that mask right though, if you release the mouse to early the aspect ratio gets locked and you need to try all over again by removing the mask and putting a new one on.
Masters in PowerPoint quickly balloon into monsters, especially when you have Frankesteined (what?) a few presentations together. The Keynote master management is a lot cleaner, also making it easy to define standard shapes and data chart formats.
Data chart creating suffers from the same problem in both PowerPont and Keynote, the first chart appears with horrible chart fills, grid lines, tick marks and always need a lot of work to get it right. I think here PowerPoint has the upper hand with the built-in Excel chart engine. This engine also allows you to do some quick analysis on the side. This comes at a price though, I find the PowerPont/Excel combination often crashing when I do complex data chart analysis. (Oh, and there is that annoying double shadow in Keynote that requires some skill to get rid of)
And finally, Keynote has tight integration with the iPad, making it easy to use a tablet device in one-on-one meetings. The iPad application also enables you to make slide edits, but because of the small form factor I expect those to be limited to correcting a type in the name of your client a few minutes before the meeting.
So in summary it is probably a narrow win for Keynote. But both programs have a few small things that still need to be ironed out. Obviously there is the learning curve to switch software. It took me probably a day to become fluent in Keynote, something that might take a bit longer if you are not a professional presentation designer...