It is a question that comes back all the time: PowerPoint or Keynote. I have given my opinion in the past.
After I got my first Mac, I was really excited to be able to design in Keynote. Now, a few years later, I must say that both products are more or less the same to me. Keynote is cleaner, auto-aligns and distributes objects when you drag them, and does not have the problem of drawing guides that you move by accident, and has a tight integration with the iPad. PowerPoint has a more convenient photo cropping UI and a much better data chart engine (Excel).
But workflow is a very important consideration as well. If the people in your organisation find it difficult to get up the learning curve with Keynote, why torture them? This is especially true if people need to do a lot of copying back and forth between Excel and PowerPoint. Probably 90% of presentations are quick and dirty documents to discuss business data, and in those cases tight integration between the 2 programs is a big time saver.
In the end both applications can deliver exactly the same look and feel of presentations. When I tell clients that Keynote presentations do not automatically look better than PowerPoint ones, they are surprised.
So in short, it actually does not matter what software you use, it is your design that matters.