It all depends on what you want. If you have plenty of time, and are willing to learn quite a bit about hardware and how everything works together, there you should build a custom AMD system. If you don't know much about computers, and don't feel like putting yourself through the torture of figuring out what works with what and what you need, probably go with the dell.
Almost all of us can help you choose parts, but I have to admit, it will take some time for you to learn and choose proper parts.