Actually, I have both the Kindle Fire and I think the Kindle Keyboard 3G. For reading pure text, the 3G version is fine as long as the publisher isn't a freaking idiot. A publisher who shall remain nameless decided to simply put his computer book (about $50) out in Kindle format with no changes. Unfortunately for me, the code samples in the original book were printed in blue with a gray background.
You could tell that there was something there, but it was impossible to read anything. Amazon took the book back and credited my account. The Kindle Fire on the other hand has color support. I have not tried that book again because I don't want to tempt the fates - and it did not work on the Amazon PC kindle reader. If color is important, then choose the Kindle Fire.