When I first started busing to downtown, it seemed like the 7 express was the best way to go. It cuts left at Dearborn, avoiding the congested Jackson corridor, and arrives about 10 minutes faster.
But there are only eight 7X buses in the morning with ~30 min headways. Why wait?
Now I take any bus at all along Rainier to the I-90 overpass. From Columbia City, the 7 local and the 9 take you there. South of I-90 on Rainier, in heavy traffic, it seems like the express is mostly just as slow as the local. So no real difference there.
On the overpass, the I-90 express routes are frequent, fast, and easy to access. They have their own dedicated lane direct to downtown — and many go straight into the bus tunnel. Hands down, they outpace any bus that moves through Dearborn or the International District.
On the way home, I start in the bus tunnel (it's dry, comfortable, well lit), transfer at the overpass (also dry & well-lit), where I can catch any of the 7, 9, 42, or 34.