I have done both. Dog sledding with the carts with wheels at the Seavey Kennell and flew up to Norris Glacier and did the real dog sledding on the snow. The real dog sledding was $320 a person 2 years ago and I think it's more expensive this year. It was great fun but because of the price I won't do it again. I now know what it's like to stand on the runners of a sled and have 12 dogs pulling you with all that stregnth and power.
The Seavey tour was fun too and tons cheaper. I think it was $30 or $40 a person? You get to ride in a cart and still get to feel the power of those dogs pulling you. Just no snow and no standing on the runners of the sled.