I personally dislike both approaches, and find that for any trip under 10 days to two weeks, a backpack is the best option. That being said however, when Weber and Malakhov made the first human powered round trip to the North Pole, they used two small sleds each. Actually, it was four sleds doubled up so that you would get two enclosed containers. They used just regular store bought kid's sleds.
That way the contents was safe if the sled turned over, the two enclosed sleds could be pulled in line together, or separated so they can be moved in relay over more difficult terrain. I also imagine the smaller sleds would be easier to pack. Anyway, I don't know if it is the best option for what you had in mind, but I thought it was interesting.
By the way, FWIW in their book, they also point out that on their failed 1992 attempt, a third member of their group tried to use a toboggan, which proved to be much less efficient than the sleds.