Based on the t17+ specs the hashrate of this unit is around 64Th/s with 3,200w and the s17 hashrate is around 53Th/s with 2,385w.
Check the whole specs of these units below
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S17 specs-
T17+ specsSo based on their specs s17 is a bit more power-efficient than t17+.
How about the price of these units and your Electricity rate?
If the price is the same and you have a free power source then choose t17+ or buy s17 if you are paying above $0.04kw/h.