We have several Kindle Fires in our house. We love them. We are big readers around here, so they are primarily used for that purpose. I don't find them heavy. You can also access the internet, watch movies, listen to music, use apps for games, calendars, contacts, etc.

My mom and sister use Nook and like them equally. I don't think there is much difference in the brands as far as capability.

I got an iPad through work this year though, so I passed my Kindle on to my husband and I use my iPad for my reading (still can access my Kindle books using the Kindle app which works well for me.). Now that I have an iPad, I much prefer using it. It has quite a bit more capabilty than the Fire, is easier to use for internet, etc. The iPad, by the way, is heavier than the Kindle.