I am going to be ordering the babies some of this, but I have no idea which one is better

I was just wondering which one you all use? Does both the Gel and the Spray work about the same? And which one is easier to use? Stedman HATES having anything done to his teeth, so should probably go with which ever one is easiest (and QUICKEST) to use on them.
P.S. - About how long did it take for you all to see results with it?
Thanks in advance