Arrange for a discount taxi to take you directly to airport. It is not going to cost much more than transferring to the Airport Express. The only benefit for taking the AE is in-town check-in, but as others said, you're going going to save much time that way either, as traffic to the Kowloon AE station may be bad.

And there is absolutely no point of transferring to the AE in Tsing Yi. Not saving you time or money, while adding a transfer.