I've ridden between Portland and Kelso three times in the last decade, always part of a longer tour. I look at Portland-Kelso as a "getting to somewhere else" ride vs a ride in itself. I pretty much agree with the assessments made by other commenters regarding the different route options. I've done them all: Oregon side via 30/Longview Bridge, Washington side via Green Mtn Road between Kalama and Ridgefield, and Washington side via I-5 between Kalama and Ridgefield. Of those three choices, I liked the WA/I-5 one the best. If I do a tour north towards Seattle again (and I probably will) I'd opt for that route. But the better riding would definitely be north of Kelso-Longview.