What are you using the PC for? Just general productivity/gaming, or will you be doing something CPU- or RAM-intensive like video editing or 3D modeling? Also, what's your screen resolution?
Either way, it's nearly always better to build yourself. You'll get the exact parts that you need/want without having to deal with subpar generic parts, preinstalled bloatware, and awful customer service.
"'Casual games' are something the 'Game Industry' invented to explain away the Wii success instead of actually listening or looking at what Nintendo did. There is no 'casual strategy' from Nintendo. 'Accessible strategy', yes, but ‘casual gamers’ is just the 'Game Industry''s polite way of saying what they feel: 'retarded gamers'."
-Sean Malstrom