I agree with your choice, I am a big Marriott SkyCity fan. Just a few notes based on my personal preference and experiences.
Since you have no status, you might also consider the Novotel CityGate if it has some decent rates. I rank the Marriott first with Citygate being second...ahead of Regal.
You asked about breakfast, the Marriott breakfast is great and very expansive....also very expensive.
Someone mentioned the Marriott counter and private transfer, that is only for people with status.
The Marriott also has a shuttle service to the Citygate Outlets and Tung Chung MTR. From there you can walk over to the Ngong Ping 360 cable car which will take you to a small village with some touristic shops, eateries and the Tian Tan Buddha. If you wanted to do something on Lantau Island before heading to Hong Kong Island.
I would just do a taxi from the airport hotel to the Conrad as the AE loses its luster the more people you have and when adding the transfer from the station to the hotel. Also, depending on the age of kids the cost might not be that much different. That is a personal preference of course.