I've done both sides, and as an impartial (New Yorker) reviewer, I have to say "it depends". If you are in a hurry, I 84 is the way to go. There are lots of waterfalls, although
Multnomah Falls is the only one you will see directly from the Interstate.
The Washington side is mostly 2 lane, and has some interesting attractions. I spent an afternoon at the
Maryhill Museum of Art. Very surprising to find a number of Rodin sculptures well away from a large city. There is also the Stonehenge WWI Memorial. Both are within a short drive of the Maryhill Campground.
As I said, I've done both sides. While I enjoyed the stops along the Washington side, I usually end up on I 84 heading to the eastern parts of Oregon.