We have demo'ed a few units including 2 flavors of Thinkpad and Transformer slider, and Transformer with doc.
Transformer with doc- Doc is pretty cool but useless most of the time. I dont create any documents on the tablets so the dock made it too heavy. But the tablet it's self is snappy and has a fantastic screen. Wider than my ipad 2 and looks clear just like the ipad. The texture of the shell is so much better than the ipad making it easier to hold and manuver.
Transformer slider- A bit clunkier than the other one with doc. It looks to be close to the regular transformer except it's thicker and not very easy to hold while laying on the couch.
Thinkpad- Really good interface, I like Lenovo's navigation system. But this tablet is thick and clunky. The screen is not as bright and vibrant like the Asus.
Of the 4, Transformer, Slider, ipad2, Thinkpad, I think the Transformer is the best. Nice clear wide screen, textured body, Android navigation, Optional Dock for when you need to compose emails.