Are you sure you want to buy a prebuilt? They are overpriced, underpowered, and very unbalanced.
Both of those machines are HSA, so it's really easy to build your own. What's more both are A8 not A10 - you can make an A10 build for £270 easily - an A10-7850k is £100, a top of the line A88 motherboard for £50, 2400MHz ram is £6 per gb, a good PSU is only £30. So that's pretty easily under £270 and has much better performance than any of those prebuilts. Using A10/A88/2400MHz would be MUCH more powerful.
If you really have your heart set on a HSA build, that's the way to go in my opinion. You can get a tiny little micro ATX case - it would fit in a show box. Otherwise, read the sticky for this subforum, and it will link you to a website called logicalincrements.com where it gives advice on what parts to buy for your budget.