Phantek looks to have good cable management which is more important than you think. I see it has tool-less HD trays, plus it has dust filters for the intake and exhaust grills, which are soooo helpful also. The Coolermaster is plain and simple - You get what you pay for.
Overall it does come down to your preference. I prefer the looks of the cooler master but the phantek look better in terms of functionality. Just because the cooler master does not have dust filters you can always add magnetic dust filters. Personally out of those two cases I would go for the phanteks because of the better cable management and dust filters. For £50 there are a lot of options. You are comparing cases from two different price ranges and if you are spending over £50 on a case then you will get what you pay for from a trusted brand.