I frequently whisper in my son's ear, 'you are my favorite, don't tell your brothers'.
The truth is: my guys know that I play favorites. I haven't fooled them at all. I have my favorite son to take to the bookstore, my favorite son to play me the violin (his brother's never got past twinkle), my favorite to snuggle with, my favorite to take out for a cup of coffee, etc.
Trying to treat each of my children exactly the same without any favoritism communicates a void of individuality. Why have more than one child if I am going to treat them like the same person? It communicates: 'Your desires, skills, and interests are not important enough to set you apart from your siblings, instead you should be just like everyone else'. That's not the message I want my guys to hear.
It is healthy to play favorites. Not only does it give me unique bonding moments with my guys, but it also requires me to study and know my children. Taking my welding son to a violin shop is not fun for him, and he's not my favorite to do that with, so we don't go. Instead, we go for coffee, and I take my favorite violinist to the shop. In the end my sons see me see them as uniquely gifted individuals worthy of my time and attention. Besides, they all know who my true favorite is... dad.
With all of the tricky navigation of homeschooling young adults don't forget to take your high schooler aside, whisper in his ear, ' you are my favorite....', and go do something together.