Would it have something to do with your age? Nothing personal, and I think the MERs are great too, but for me Pioneer 10 and 11 were a highlight for me, being among the first space probes I remember in detail.

Talk about your major accomplishments: The first ones past Mars, the first ones through the Planetoid Belt, the first ones past Jupiter, Pioneer 11 was the first one past Saturn, and the first ones into interstellar space, carrying a message for any ETI no less. Yes, I know Voyager 1 beat Pioneer 10 a while back for the distance record, but the Pioneers were the first ones out there.

And to add this, Pioneer 10, launched in early 1972, kept transmitting to Earth until 2003.

http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNhome.html