For all round versatility I would probably go for a laptop. For portability go for a 13 or 15 inch.

I have an Iphone and a laptop. The Iphone tends to get used for calls, mapping, emergency browsing when I'm out and about. But all the serious stuff like word processing, spreadsheets, BBC I Player etc is done with the laptop.

It also depends on how long you want it to last these days as no matter what gadget you buy it will probably be technically obsolete in six months (probably sooner!).

CC