You can't go wrong with either. We loved dinner there. The food was good, it was fun meeting the beast, and there isn't as much hustle and bustle around you as there is at lunch when it is CS and people are walking around constantly.
But...we love lunch there too. If you can't get a dinner ADR or it doesn't fit into your schedule, you should definitely go for lunch. The line can be deceiving, sometimes what looks for sure like it is an hour long line is only 15 minutes. Just ask a CM standing in the area and they can tell you how long it will really take to get through the line. We've gone during the noon hour and the line was so long that DH swore it would be well over an hour and did not want to do it, but the CM said it was only 20 minutes, and it turned out to just be 15. It was well worth the wait!