Which will perform better?



Yes i would but since i've been looking around i've struggled to find anything cheaper than these
 


What's your budget?
 


Around the same as these, no more but it'd need windows and wifi adapter
 
Pre-built PCs tend to cheap out on the PSU & motherboard (and on the Zoostorm PC, it doesn't even appear adequate wattage at 350W! It would really need to be running at Platinum efficiency - which I can guarantee it would not)

Pricing the parts, including a quality PSU & decent motherboard, you'd be around £600-650

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i5-4460 3.2GHz Quad-Core Processor (£140.10 @ CCL Computers)
Motherboard: Gigabyte GA-H97N-WIFI Mini ITX LGA1150 Motherboard (£95.26 @ CCL Computers)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1600 Memory (£41.99 @ Novatech)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£34.74 @ Aria PC)
Video Card: Gigabyte GeForce GTX 960 2GB Video Card (£139.90 @ Aria PC)
Case: Thermaltake VL80001W2Z ATX Mid Tower Case (£34.82 @ Dabs)
Power Supply: EVGA SuperNOVA G2 550W 80+ Gold Certified Fully-Modular ATX Power Supply (£66.60 @ Amazon UK)
Optical Drive: Samsung SH-224DB/BEBE DVD/CD Writer (£9.38 @ CCL Computers)
Operating System: Microsoft Windows 7 Home Premium SP1 OEM (64-bit) (£67.95 @ Ebuyer)
Total: £630.74
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-09-28 17:56 BST+0100

I really don't see where their profit is in those builds. Normally you'd see an absolute minimum 15-20% 'mark up' for pre-builts, so I would seriously question the quality going into those builds, for the prices listed.

Personally, I'd suggest adding a 250GB SSD (http://uk.pcpartpicker.com/part/samsung-internal-hard-drive-mz75e250bam) for an additional £70 and build it yourself for £700 - although there's likely some changes that can be made to the build to improve price and/or performance.