I've found Lyft w/ Wait & Save (~$35 + tip) to consistently be cheaper to Downtown Seattle compared to Uber (~$45 + tip), often beating the Flat Rate Cabs ($40 + tip). Doesn't beat light rail on cost, but then you're on the train for 40 minutes so ...
The double dip with Chase cards (10x CSR, 5x Freedom/Ink/etc.) is nice too.