I have a 12" C-Series on my A-5 and I love it. I also have the Apex Tip on it. With Nelson HotSpots, Special Forces, or Visible Impact, I can hit a mask @ 50 feet 99% of the time.
Read this thread:
Panda86's barrel tests
If however you are looking for the most accurate barrel, you would want to go with a barrel kit so that you can match the Bore to the paint you are using. I don't have a lot of experience with kits, so someone else jump in here.