I've done both. The route via the Siberian pass junction and Rock Creek trail is _much_ nicer than the PCT. The PCT isn't bad and has some more expansive views to the South and West, but Rock Creek is a really beautiful hike with plenty of water, some very good camping, and another couple of lakes to swim in.
Thanks a ton for this, very useful.
I'm doing a one-way trip so can't do both.