The top one is the older version, originally this one was done in yellow with a dark blue blue front(Yellow is the limited edition, only 500 were made in the first batch)
Then it was released in black and then blue(top picture), blue is just the new giant colour. I think the black and blue ones are the same other than the colour, the difference from the yellow one is minor changes such as the rear disc mount etc.
The bottom one is the newest frame which is a different shape.
I have the original yellow one, Had it for 4 years and its solid. Very light and short so nice and easy to hop around. Has a good reputation from what I hear from people personally.
Harry - Littleharrys@hotmail.com