I have Kindle 1 and would recommend it. But both are solid e-readers. The Nook has some complaints about being a bit slow and clunky, lag between the small color screen and the e-ink screen (as e-ink is slow to refresh, just a limit of the technology) etc. You do get the book sharing option. Though if you're just sharing with your wife etc. you can share kindle books by having multipe kindles (or Kindle for PC programs, or iPhones/iTouches with Kindle App) linked to your account. All will have access to all books you buy--each book has a limited number of devices it can be downloaded too--usually 5 or 6. But the limit is up to the publisher.
The Amazon store has a bigger selection (though most books you'll find in both stores--so unless you're after something pretty obscure it won't affect you most of the time) and when there's a price difference on books I've checked, Amazon tends to be a little cheaper (but usually not a huge difference, a buck or less most of the time).
And being tied to one store isn't true of any device. There are stores out there like Fictionwise that sell non-DRM books. Any not DRM .mobi book will work on the Kindle, or you could buy in a format for the Nook or Sony. Or you can convert them into the format you need using a free program like Calibre. Also, even with DRM books, you can google and find the software (free) you need to strip DRM and then can convert it to the format for your device with Calibre.
In short, both are very good readers. I'd go Kindle personally. Plus Amazon has a 30 day trial period. So if you don't like it you can send it back for full refund and just be out the $5 or so that it costs to ship it back.