I've developed nearly a hundred presentations in a professional capacity (not as in, I made presentations for meetings at work like everyone does but as the actual end product at a marketing agency) in both Keynote and Powerpoint and find Keynote is much faster to work in than PowerPoint - the fact you can work with vectors is huge, and the application rarely gets bogged down when working with huge files. PowerPoint does have some awesome features I'd love to see come to Keynote, but it still takes significantly longer to get the same quality output.
Numbers has nothing on Excel for flexibility and depth, and the same is true for Pages on Word outside of desktop publishing ...but Microsoft has Publisher which is more powerful for desktop publishing too. In that case - do you want a simple tool that does a little of both, or two separate tools that are more complicated but do much more? Are you working on a brochure or one off item? Or is it a monthly 125 page magazine?
And of course, are you more comfortable with Apple's UX approach or Microsoft's UX approach? You can click between a dozen panes till your fingers are sore, or handle more ribbons than a rhythmic gymnastic competition. Pick your poison.