And do you want to buy a pre-built ready-to-go system, or build your own. Pre-built is cheaper, but gaming may be an issue due to the lower quality parts. Building your own from the ground up may be a bit more in the long run, but you have the benefit of using better components and have future upgradability.
We need a lot more information from you to point you in the correct direction. First let me state that building your own pc is much better than purchasing one that is already built. On that note if you want the ultimate bang for your buck then try going that route with building yourself it's easy. If you don't have experience building you can easily watch YouTube videos on how to do so.
Other than that what games exactly would u like to play/run.
Do you plan to do over clocking at all? Lastly we need a budget