None of them, they're all horrible. Building your own PC is far better than getting any pre-built. The problem with pre-builts is that they usually have no named PSUs or HDDs, have a high end CPU with a low end GPU or vice versa, and are just horrible quality overall. I'm guessing your budget is £700? Does that include OS, peripherals? What games will you be playing? Do you intend to overclock? Do you want to build your own, really the only option for gaming PCs tbh.