As someone said: it all depends
If, like me, you are a long-time user of Word, Excel, and Powerpoint, then you will probably find Pages and Numbers less fully-featured and, because of the different interface, with something of a learning curve. Keynote is generally reckoned to be better than Powerpoint, but so far I've only used it once, so can't really judge. In trying to use Pages, I keep getting stuck on figuring out how to do something that is, for me, relatively straightforward in Word (although I hate the new interface for Word). So, I may start something in Pages and then say, Oh the h... with it, and open it in Word to finish.
If, on the other hand, you are starting out all nice and fresh, it really wouldn't matter which you used, unless you were a major user of complex spreadsheets, in which case, Excel still beats Numbers.