I've hiked the length of the park south-to-north some years back, and as part of the Pacific NW Trail I more recently hiked it from west-to-east. That said, I'm not familiar with the (vast?) majority of this large park. To get a good answer to your question, you need someone that has hiked lots and lots of trails in the park AND whose response you can calibrate in the context of your personal abilities and desires for a "best" trail.

I've really enjoyed coastal hiking in the ONP. The reference in another response to the high divide/low divide --- I hiked the high divide in a lot of snow in hiking the PNT, and that Seven Lakes Basin area really is pretty neat (but also as I understand it, pretty popular).

It's a tough question to answer. One thing in the ONP that's on my personal bucket list was a route variant that had too much snow to be safe when I went through --- the Bailey Range Traverse. Looks somewhat aggressive, but in the narrow window that it's hike-able, just a stone hoot I think. Someday perhaps!
Brian Lewis