Here is a ROI comparison for the Bitmain Antminers if you are considering them:
Clearly the V9 brings home the game, due to its low initial investment cost at only $86/THs, compared to the $172 for the S9 and $191 for the T9. In essence the V4 gives you almost double the TH capacity compared to the S9 and more than double compared to the T9. The price you pay is higher cost of power, but in the above comparison - with a low cost of power (Sverdlovsk Oblast, Russia) - the V9 still brings home the game in the 24 month scenario. Please note that the total earnings/profit is discounted with 25 % for the expected increased difficulty that most calculations like these omit.
It is important you consider your cost of power, as in this example the V9 cost 2,6 TIMES more than the S9. If you are in a high cost area, this could tip to favour the S9 over V9. The T9 is in-between the two, but closer to the S9.