I have a 3rd gen. I love it, and DH who is the household geek is very impressed with the quality of the screen over earlier models. So if you want to play games, photo editing, video, that sort of thing, it might be worth paying more. Also I have noticed more apps are only stating they are compatible with the most current model. I think that is true of most tech.
We also have an android Eeepad and a Playbook. Having seen what is available on these, it tends to be far more limited, often more expensive and the screens are nowhere near as good. Not always, but that's my experience.
DH came home with a Mini from work last week and it is delicious. So thin and light, great screen, perfect if you want portable. I was very impressed with it. For small you also have things like the Kindle Fire, but then you are tied to Amazon. That's going to be an issue no matter what you choose though.
Personally I am very impressed with the iPad. I would go with a mini or the 3rd gen depending on finances. I also find that web browsing in general is better with Apple.
Go and have a look somewhere that stocks them all and see what you think, in the end there's no point buying something you aren't happy with and which suits your needs.