Microsoft Surface Pro 4
Let's get right to the big one: the Pro 4. This model has a lot going for it in the 'battle of the Pros', as it can also use a stylus, a clip on keyboard, has a similar-sized screen but also offers a full desktop experience. It's slightly cheaper too (starting at 128GB models) and comes with the pen included - but the power and storage options go way higher (as does the cost… ouch).
What it lacks is the App Store offerings that the iPad can take advantage of - there's so much here that can alter your iPad in a heartbeat, taking it from one type of machine to another, and really dedicating it to one task.
It depends what you want. If you're after a targeted, fluid tablet-centric experience then the iPad has the lead. If you're looking for the full desktop way of doing things, then that's where the SP4 sits.
iPad Air 2
You're thinking whether you need all that extra space in your hand. Do you want the extra speaker power, the ability to type on the go or sketch down notes?
To some people - probably not, and they'll still be able to pick up the iPad Air 2 (for less cash too). It still runs nearly every app with power and grace, and while the screen isn't as immersive thanks to the smaller size, it's slightly more portable. It's a shame you can't use the Pencil here, but there are styluses and keyboards available from third parties if you fancy that.
iPad Pro 9.7
Apple's seemingly killed off the iPad Air range, launching a 9.7-inch version of the iPad Pro in place of a new entry. As such the iPad Pro 9.7 has many of the same selling points as the Pro 12.9, including optional accessories like the Smart Keyboard and Apple Pencil.
It's powerful too, with the same A9X chip, but just 2GB of RAM - that's half what the iPad Pro 12.9 has and shows the slightly 'watered-down' angle of the smaller device.
The main differences though come in the form of a lower price and a smaller screen. The former is an undeniably good thing, but the latter is more debatable.
If you just want a general jack-of-all-trades tablet that you can easily carry around with you then the iPad Pro 9.7 is the smart choice, but the smaller size means it lacks some of the productivity potential of its larger sibling, despite the 'Pro' monicker and the accessories that come with that.
Sony Xperia Z4 Tablet
Android's best tablet-cum-word processor is worthy of inclusion here as it offers something different to the iPad Pro. Firstly, Android is a more customisable experience, letting you move files around and change the way it looks with ease.
Sony has also accessorised the OS to let you use a pointer with the keyboard to navigate around the display, something the iPad doesn't have in its wheelhouse, and I would have sorely loved it on the iPad Pro to not have to keep jabbing at the screen with less precision than mice afford.
The Z4 Tablet has a great screen, is waterproof and is cheaper than the iPad Pro 12.9 by a few hundred dollar bucks - but lacks the capacity, grunt and size the Pro can bring.
Samsung Galaxy View
I've included this just because it's a big tablet from Samsung, but in reality the two aren't competitors at all. The View comes in at 18.4-inches for the screen, is a portable Android tablet that's seemingly designed exclusively for the house and doesn't have anywhere near the screen resolution.
That said, it's half the cost of the base model iPad Pro 12.9, and if you're just looking for a tablet that can replace the TV around the home, or function as a second device, this will do the job for less cash. However, it's a lot heavier and has a bolted-on kickstand, so get working on those shoulders before purchase.
The Nexus 9 is the cheapest option here (around a third of the price of the Pro), simply because it seems Google has forgotten about its flagship, HTC-made tablet.
It has decent front-facing speakers (thanks to the affiliation with HTC) and comes with an optional keyboard to turn it into a more laptop-esque experience. You can pick up styluses for it, and of course it runs the latest version of Android, so you'll always be up to date with your software.
It's a smaller screen though - even lower than the iPad Air 2 - so be ready to squint a bit more if you want to save some cash.