Hi Brenda - That's a really tricky one, as there is a lot of crossover between the RowCruiser and the Expedition. It really comes down to what your exact needs are. Boat design is all about compromise, neither does great with everything. I'll give create a list of some of the core attributes of the boats, and how each compares to the other.
Cargo Carrying: While the Expedition is excellent in this realm, the RowCruiser is even better. The Expedition carries about three times what a typical sea kayak can carry, while the RowCruiser can carry twice what the Expedition can. The large central cabin of the RowCruiser (and extra large hatch) allow you to insert some pretty sizeable items into the boat. The Expedition also has a large hatch as well, but not quite as big.
Passenger Carrying: In calm conditions you can place a passenger in the mid compartment of the Expedition, however, it is not ideal. The RowCruiser, however, can comfortably carry a passenger in the sleeping compartment. It's very comfortable here and sheltered from the elements. A couple of small kids can also squeeze in here. Additionally, kids up to about 12 can fit in the rear compartment with the hatch lid off. So definitely the RowCruiser is the winner here.
Speed: In calm conditions the two boats are pretty close. In heavier winds and waves, however, the Expedition is the clear winner. The extra weight and windage of the RowCruiser does slow it down.
Transportability: The Expedition is easier to transport, being a little lighter and smaller.
Time to Build: The Expedition is a little less complex, so is quicker to build, and requires less materials.
Seaworthiness: If you're going into really rough conditions, the Expedition is slightly more seaworthy for two reasons. The first is because you can keep making way in rougher sea state (being able to move towards safety is an important part of a seaworthy boat). Secondly, with simpler hatches, it is easier to ensure it is fully watertight so doesn't take in any water.
Cost: Being a bit smaller, the Expedition will cost about 20 percent less to build.
I hope this helps somewhat. I know choosing the right boat is always tough. It's all about really thinking what you want to do with it, and what's going to serve those needs best. Good luck!