In my point of view, the BTC/USD is in upward trend. All the time growing difficulty. The difficulty of course is derived from the BTC/USD and the installation of new equipment. Old equipment is also working due to an increase BTC/USD. Accordingly, the difficulty will continue to grow.
This means that in my opinion at the moment the best is to buy BTC. Those who possess miners, when the difficulty was relatively stable already earned and have a different position than those who are just starting in this business. For the purchase of miners it is worth to wait for difficulty stabilization.