In the end use your judgement to decide how you're going to employ your device for the majority of the time, and the things that are the most important to you, then you'll no doubt be happy with whichever machine you pick.
iMac vs MacBook Air: The current MacBook Air range
Apple has kept the MacBook Air range very simple in recent years. At the moment your choices are straightforward and really come down to the size of screen that fits your needs. The two variants - the 11in and 13in - both share the same 1.6GHz dual-core Intel Core i5 CPU, 4GB of RAM, and come in either 128GB or 256GB flash-storage options. Neither of comes with a full HD screen, so if you're looking for the Retina display you'll need to turn to the MacBook Pro range or Apple's new MacBook.
You can buy the 11in Air with 128GB of storage for £749 or 256GB for £899, and the respective 13in alternatives are each £100 more, at £849 (128GB) and £999 (256GB). On the Apple website you can also use the built to order options to upgrade the CPU in any of the machines to a 2.2GHz dual-core Intel Core i7 for £130. This is a decent upgrade, but we'd advice you leave this and increase the amount of RAM instead, as it can't be upgraded later and could become restrictive far quicker than the existing i5 CPU. Moving from 4GB to 8GB costs £80, and is something of an essential purchase if you want to really future-proof your device.
This option still applies to the 11in Air, but from April 2016 the 13in Air now, pleasingly, comes with 8GB RAM as standard. Check them out here.
A final build to order option offers 512GB flash-storage for £240.
If you're not planning to upgrade any of the MacBook Air components when you buy, you don't have to purchase from Apple. You'll also find the MacBook Air available from the likes of John Lewis, Currys and other third party retailers if you prefer.
iMac vs MacBook Air: The current iMac range
Things are a little more complicated on the iMac side of things. There are still two screen size options - 21in and 27in - but each model within those variants comes with a different CPU and graphics capability. You can also decide whether you want to cough up the extra cash for the Retina 4K display for the 21in model, while the 27in is now only available with the impressive Retina 5K display.
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