Our family has Kindle Fires and the original Nexus 7 tablets. We definitely like the Nexus tablets better than the Fires. BUT - my son won a Asus Memo Pad HD7 ME173X from school yesterday, and I have to say I am really impressed with it. Essentially the same as the Nexus 7, but it has an sd card slot. Awesome. Charge port is on the top instead of the bottom - good idea. If I were to buy another tablet right now, that's what I would recommend.
For those who miss using the keyboard when using a tablet --- I use a bluetooth keyboard from ebay for my Nexus - pretty cheap, and makes typing a breeze.
You can actually connect a SD card or USB to a Nexus 7 - I do it all the time. It's not as pretty as devices that allow you to just insert an SD card into the device because everything is external, but at least for me, that's not a big deal given what I use the SD/USBs for (a store of movies, pictures, etc. - I don't need to keep apps or app data on them. If I need to use something that is on the USB/SD, such as a movie, I just copy it from the USB/SD to my Nexus 7, then delete it off again when I am done to free up the space on the device.)
To make it work, get the app "Nexus Media Importer". You will also need a USB OTG cable (USB 2.0 Micro B Male to A Female OTG cable to be exact) - you can pick these up for a few bucks on eBay or
Amazon. If you want to use a SD card instead of a USB, you will also need a SD card reader - you can also pick those up cheap on eBay or Amazon.
There might be a setting you need to enable to allow writes to the SD/USB, if you want to do that - if I remember right, the default is that only reads are allowed. But just go into the app settings, and you'll see what you need to change. (I use that feature to keep a backup copy of pictures as I am travelling - I copy pictures off of my camera nightly to the Nexus 7, then move them from there to a USB for a backup in case my camara card goes bad.)
[Note I suggest buying a multipack of the OTG connectors, and more than one SD card reader because they all tend to be cheaply made, and go bad easily. Whenever I've had problems with the Media Importer app not working, it's actually been a problem with either my cable or SD card reader, not the app itself. I also suggest using a USB instead of a SD card whenever you can because SD card readers just seem to be fussy in general - but I do use a SD card reader to import pictures from my camera to the device, so I know it can work when the SD card reader cooperates.]
One of the biggest advantages to the Nexus 7 is that you get Android updates faster than anyone else. Other manufacturers overlay stock Android with their own stuff, so it takes them longer to push out updates. As with all hardware, the Nexus 7 will become desupported at some point and will stop receiving updates, but I expect that the life of the Nexus 7 will be longer than similar devices from other manufacturers because of this overlay issue.