The best would really to build a pc with 3 or 4 of the best video cards for mining Bitcoins in it.
Error. No GPU will mine Bitcoin at a profit or even close, and even with FREE electric the cards will die before you ever made back enough to pay for them.
Ditto for any other SHA256 based coin.
Scrypt is almost as bad.
non-Scrypt non-SHA256 coins are where to look at if using a GPU, though it appears that X11 (and possibly X13/X15) days of GPU mining for profit might be ending soon, *IF* the recently-announced ASIC miner for them turns out to be real and not vaporware/scamware.
Unless you have VERY VERY cheap electric, or FREE electric, you won't make ROI on any currently available ASIC Bitcoin miner at this time. The upcomming 14/16nm full custom generation might change that.
Scrypt with ASIC is viable right now even with not-real-cheap electric, if you go with any of the used A2 or Alcheminer units around, and POSSIBLY with the used Titan units around *IF THEY LIVE LONG ENOUGH* (the Titans are pretty notorious for their mining chips having dies go dead far too often, the A2 has proven to be a tank that just don't quit and the Alcheminers seem to have good long-term reliability as well but haven't been around nearly as long).