I-40, for now. It's in pretty good shape for heading West from Downtown.
Henley Street Bridge seems to always be congested.
There is major work being done on the James White Parkway/I-40 intersection and that clogs up I-40 heading East, often just before the merge with I-275. Heading home, may need to get off at Western and get to Henley that way.
You might want to try cutting over to Gay Street at Baptist Hospital, picking up Neyland Drive and taking that to Alcoa Highway and then heading to I-40. The work at Papermill is finished and it moves a lot faster than it used to.
Pellissippi Parkway might be fastest, depending on where you are. Cut over to that on Topside Road from Alcoa Highway.
You can check here for traffic:
TDOT SmartWay