You also have to remember that GNS3 requires the Cisco IOS files, something not everyone has access to, where as more people can easily get hold of PT. I have tried both programs and for me PT was simply better, it covered the full Cisco Accademy CCNA material and just worked, where as when I tried GNS3 I had to find the suitable IOS files, then decide which ones to use based on which feature set I wanted, and even once I got the right files, it simply didn't work, the program ran but it always gave an error when trying to actully start a device.
Thats just my experience with it though. For CCNA you can't realy go wrong one what option you chose as its quite basic stuff. When you get on to CCNP though and deal with things like layer 3 switching and such, then you may have to look more closely at work programs offer what features, or maybe even building your own lab from old cisco hardware.