I highly recommend 1050TI, you can build an 8+cards rig of it which costs less than $2000. it is the most flexible and valuable card I've ever used
Not to rain on your parade, but you should really look at power efficiency comparing a 1050ti rig to a 1070 rig.
While your 1050ti rig may be cheaper, a 1070 mining rig is more efficient and will earn more in the long run. Also, it is easier to sell 3-4pcs of 1070 GPUs compared to having to sell 8pcs of 1050tis. Configuration is easier with 1070s too.