I picked up an OPC rookie, figured it was a bit more fun than a Topps and just as condition sensitive.
For me the best RC regardless of value is the 1990 Leaf because I recall what an intense year that was for new cards, and that set was the hot set. I wasn't willing to spend the money on Thomas, Walker and the other hot RCs and now I am picking them up for pennies on the dollar, but I still excited when I get one.