You really should give a BUDGET as the sky's the limit when you say "best."
For $1200 I could build a system with an i5-4670K and a GTX780 for example which kicks ass. Buying it pre-built would cost a lot more and pre-built's have annoying Warranty issues (don't open or void; return entire PC..).
For $200 less I'd get a GTX770 or possibly a new AMD card though I'm partial to NVidia cards for several reasons including the upcoming G-Sync monitors.
I suggest you give a budget or MIN/MAX and let some guys help with pcpartspicker. Specify exactly what it includes as well.
Again, building your OWN is definitely the way to go and there are many advantages.