I guess I'm a little late to the Pro/DWC Road running, but if you want to really go for it, go for it in S1 or S2 if you haven't already started. The A class series is really weak with a few exceptions. Only the top 15 of S1 and S2 will be considered for Pro this year.
I'd say go for Pro if you have the time, 2013 was a very competitive field throughout imo and the 2014 DWC I think really has the best of the best due to it. 2014 Pro is most likely going to be no where near as competitive. If you want always competitive fields, run GT3.