Most of my DC trips have actually been on the 600 series. Not sure what to say about getting a better experience.
For PE, I like the fact that the 600 series has the PE toilet, however the galley in front of my favourite seat can be a pain. I often get whacked with the curtain, so the 300 series layout is better in that respect.
Then plane differences in reality are minor, the crew can make or break the flight. On a couple of DC trips, I appeared to have booked on a day when they were breaking in new crew. Although they were not fully aware of all the VS process and emenities, the service was very polite and professional. Although not as relaxed and friendly as you normally get.
Enjoy DC, it's a great place.
Mark