Planning a visit to the Redwood Forests?

I've visited several of these parks, though it's been several years: definitely Prairie Creek, Humboldt, and Redwood National Park, and I think perhaps one or two others. I recall them all as being beautiful; I wouldn't say there's a particular one that you have to visit or you're missing out. I don't think you can go too far wrong.

Note that even within these parks, there are relatively few areas of old-growth redwood forest; most of the land has been logged in the last 150 years and now supports second-growth forest with smaller, younger trees, which are nice enough but not what you came to see. So within each park, you'll have to seek out the old-growth areas; check park maps or ask rangers. They may not always coincide with the locations of campsites.

I recall the trees being of roughly similar (and very impressive) size within all the old-growth forests I've visited. Of course somewhere there is a tallest tree, but beyond a certain point the eye can't really tell, so I don't think it's worth it to specifically seek out the record holders. Anyway, you generally can't see the top of a tree from the ground.

On a side note, these parks are pretty popular in summer, and campsites often fill up. You should consider reserving your camping spots well ahead. If you're properly equipped, you might think about hike-in campsites; they are often quieter and less crowded. Camping outside official campsites is generally either discouraged or forbidden.

Have a great time!