The Trout Lake to Chinook Pass section is really stunning and, to me, one of the best 100-mile sections on the whole PCT (right up there with the JMT and northern Washington). You get Mt. Adams, Goat Rocks, and the Mt. Rainier area, all of which are terrific.
The OR section you mentioned is nothing special--lots of nice forests, lots of lakes, possibly lots of mosquitoes depending on how the summer goes. Three Sisters is great, but the most scenic parts of Oregon are from the CA border to Crater Lake and 3 Sisters to Cascade Locks. For me, central Oregon was kind of boring.
I haven't done the Wonderland Trail.
If you are open to alternative PCT sections, the Alpine Lakes (I-90 to Hwy. 2) and Glacier Peak (Hwy. 2 to Stehekin) sections are really phenomenal--epic scenery. Alpine Lakes is about 75 miles, and Glacier Peak is close to 100. You'd have to take the boat to or from Chelan to do Glacier Peak, but it would be worth it.