Against tight players don't bother 3betting light - they only open strong hands so why try to make them fold?
Against laggy players it depends on how laggy they are, how they respond to c-bets, etc. If they are raising lots of raggy aces then 3bet mid aces like A9, AT, AJ which dominate their range.
The best place to use 3betting light IMO is vs laggy CO/BTN stealers, where you can 3bet fairly wide. Take notes on how they react to 3bets - how often do they fold, how often do they 4bet (and with what if it goes to showdown), how often do they peel and fold a flop, etc