Another vote for the Q-Bot's at Great Adventure. This is my "home" Six Flags park. With a Q-bot, you can easily get all the coaster credits, and walk around. Yes, it can be expensive but instead of waiting in lines for 2+ hours, easily justifies the cost of Q-Bot.
I'm also of the Knoebels > Dorney. But I understand Dorney being the choice for more coasters.
If you can swing it really consider adding Lake Compounce or Six Flags New England. Lake Compounce offers a great variety of flat rides, along with Boulder Dash (It's Boulder Dash, that speaks for itself ) And Bizarro is a great coaster.