If you want to expand on your knowledge and skills, and are up for new challenges, I recommend that you visit those ARTCCs that have complex airspaces, such as ZNY, ZDC, or ZOA. These all have major airports that are very close to each other and get a lot of traffic (e.g. JFK/LGA/EWR in ZNY, or BWI/DCA/IAD in ZDC, or SFO/OAK in ZOA). This means you not only see a good deal of traffic and gain experience, but also learn how complex airspaces interact with each other.