Here comes my opinion.
I have been an android guy for a long time now. As far as the Nexus 7 goes, it is a great "value" tablet. Blazing fast, good features. It simply lacks in speaker quality and screen quality. (btw I am not saying the screen is bad, but it is no apple retina display.) You will not be able to use your flash sites on new android tablets as well.
As for the windows 8 tablets go. I think this would be an interesting route to go, they look pretty good from my point of view. I have been playing with the operating system for a while on my laptop with the developer previews they have released and i think the OS will be very tablet friendly and the interface which they wanted to call metro(it no longer is) is really awesome aesthetically speaking.
And of course the tech giant. You really cant go wrong with the ipad/ipad mini. It all comes down to the inability to use flash based websites and the price. you could opt for the ipad 2 to save a little money. Overall the ipad would be the best device IMO to show off a collection in the gallery app and the simplest to transfer music, images, and other data to and from through itunes.(which is a pretty important ability).
Hope this helps, if you have any other specific question I consider myself pretty knowledgable on the topic.
-jnapp18@gmail.com