What's the best mining option if you weren't worried about power costs? If you had a free power source and took it out of the equation, what would be potentially the best option for bitcoin mining?

You have limited space, so for about one or two computers tops. What hardware would you choose ultimately based on the basis it's available today?

e.g. Can top end graphics cards still be as good as a FPGA setup?

Can FPGA's out do ASIC in the aspect that the hardware is cheaper/ more accessible? or is it still not worth while in comparison?
At time of writing it still possible to run a GPU farm but at the speed of the increase in difficulty this will not last for long.

The second presumption with this is that you are not paying for the hardware, its very unlikely you would even  break even if you had to purchase hardware at this time. The only real option in a competitive market is to go down the ASIC route. 

Performance in a good quality ASIC can be 100 x that of a top end GPU. The price tag could realistically be about the same. There is zero comparison.