First off, NOT THE iPad!!!
Transferring files other than music and movies is a royal pain in the ass. Also, I tried many PDF readers for iOS4 and the only one that even came close to the EX PDF Reader I have on my Droid X had a file transfer procedure so arcane that it bordered on ludicrous. iBooks was easy to transfer stuff to, but was so lacking as a reader that that strength could not save it.
When if comes to Office stuff, I can view and edit .xls files with ease using free apps on my Droid. I never tried to do anything like that on my iPod Touch because I never found a free app to do so with. Come to think of it, I think that some of the free apps I use are ones that Apple charges money for the iOS version of.
If you want an inexpensive solution, go with an Android tablet, but be aware that iw won’t quite compete with your laptop thought the portability and battery life compensate for that . If you want something that can compete with your laptop for speed and power while still being tablet-sized, you are wanting something like these updated versions of what @XOIIO has
Regardless, while the iPad is great for entertainment, it really isn’t all that good at anything remotely practical including reading PDFs so I would not recommend going the Apple route.
What size are you thinking anyways? Apple only offers one size, but Android ranges from 5” to 12”. DO you merely plan to view things (something an ARM A9 or Intel Atom could handle) or do you really need somethingthat might give your laptop a run for it’s money? In short, could you please be a little more specific about wha tyou are looking for?