I write on this subject for work. Here's a quick brain-dump:
If your wants are simple and straightforward, an iPad will do just fine. If you want something that can replace a PC, or you want a lot of storage, or to do complex, geeky things, an Android tablet is a better alternative. I'd recommend getting a Samsung Galaxy Note 10.1 (has a stylus) or a Tab 10.1 (hasn't) - both have slots for the tiny but huge-inside MicroSD storage cards. 64GB MicroSD is currently about £35 from the net.
If you've an iPhone, you shouldn't need a tablet with 3G/4G capability as you can use your phone as a 'WiFi hotspot' - this saves about £150 per device (your mileage may vary). Anything should connect to it (iPad or Android), and use it as if you're on your home WiFi. Obviously if your network data charges are high this won'tr be cheap, but it won't be better if you connect straight from a tablet.
The key constraint about an iPad is that it won't let you see the file structure inside (folders/directories, etc.). That's not necessarily a problem, but if you want to work on files as files, it can be pretty annoying. You can also use a mouse easily with an Android tablet. Both will allow an external keyboard - in fact I use our Apple one with both brands.
Don't go for a cheap Android thing - often there's poor integration between Android and the hardware - the hassle isn't worth what you will save. Do buy a soft case for it - if you go Apple, the magnetic flip over thing they sell is rubbish - I've got a Belkin one for the Galaxy 10.1 and something similar else from John Lewis for the iPad. Very much down to personal choice, but make sure the corners, edges and screen are reasonably safe from sharp objects and the shock of being dropped or put down on concrete in a thin bag.
John Lewis has keen pricing and offer a year's longer warranty than Apple Stores. Apple will set up the device in-store, but that's hardly necessary, and I'd rather ahve the warranty (I've needed it in the past on Apple products!).
It's also worth checking your household insurance policy for cover when out and about.
IPads will display Excel spreadsheets, but can't alter them without paid-for apps. Samsung tablets come with Polaris suite installed - a bit basic but it lets you make and change data in spreadsheets, make Word and Powerpoint documents too. For more detailed control you can get Open Office now for Android - it's a big and slower package, but works like the desktop older versions of MS Office (no "ribbon" ! ). Open Office is also free (there's a pop-up ad on startup but you can ignore it).
The iPad's screen is nominally better, but I don't notice a huge difference in practice - few things have enough detail to make the difference important. Regarding keeping them in-sync, say with files on your PC or contact lists on your 'phone that's as easy using Android as it is with iPads - you should be able to pass data iPhone to Android too, and in reverse.
I suggest a trip to John Lewis, ideally on a Tuesday morning when it's quietest. Tell the staff there (they sell both Apple and Samsung stuff) what you'd like to be able to do, and have a look at what's available.
I've just taken my Android tablet on a 2000 mile road trip in the USA (southern Utah and Colorado). It's the first time in more than 20 years (and 20+ trips) I haven't taken a laptop over there. It did brilliantly. I think Google's maps application is marginally better than Apple's (we didn't buy any road maps - didn't need to as we downloaded them in cafes, etc. and saved them for use later).
It's a very personal thing, your mobile computing. As I said, if you want it VERY simple, and don't mind having to do it one particular way, iPads really are good - design and in use, but if you want more flexibility: Android (or hack your iPad).
Regards,
E.
