What is the best cryptocurrency to mine for 1070 TI?

Mining with GPUs????

Anything that isn't already mining with FPGA chips (which blow GPUs out of the water) or with ASIC chips (which blow FPGAs out of the water).

Why not build an ASIC rig?

This site should help you determine what to mine with a given set of hardware. You should probably check it regularly, as "what is most profitable this week" might not be "most profitable the next week".

http://whattomine.com/