Regardless if you call it, a tablet, slate or a pad there are many different features out there. It basically comes down to what are you looking for in one. So I'm curious as to what are you looking for, what do you want?
Well the folks at Gizmodo came out with a guide as to who has what. Here's a comparison chart showing the features of an Apple iPad, HP Slate, JooJoo, Notion Ink Adam, Dell Mini 5 and Archos 7 Android:
I agree it has a full OS and Windows 7. I have a archos 5 and I do really like it but really it is to small to be a e-reader. That has linux on it. I love it when traveling but 75% of the time I watch movies on it. I have it loaded with movies
Thing I want to know is, the Nook and Kindle are using some sort of 'electronic ink' display, that makes it more like reading actual paper, and is also supposed to be easier on your eyes for the same reason. I'm guessing none of these do that, including the Apple iPad?
That alone may be a good reason to go with a dedicated eReader if that's your main concern.
Olympus
Single & Not Looking
Going by that list, the HP Slate seems to be the best one.