I regret not spending more time with my kids eg. Putting work or going out ahead of them.
And I have quandaries, too - my A is very challenging at 18 and I wonder whether being stricter or more laid back would have made a difference. I'm tightening up on mobile ph use for the other kids because her addiction to it has meant no HSC for her (she began skipping school ti Facebook and watch movies on her ph).
I regret allowing A to go to Boarding School for a year - she was the one who begged to go (and to come home at the end if the year) but it only seemed to make her resent everything (esp her family) and pick up dodgy habits (like the mobile use).
I sometimes think that I've taught my students better than I've taught my own kids in a number of areas - comes back to spending time with them, I guess.