Daycare all the way in my households. When I first got the game I hired one (she is still alive in my game AND the only nanny) but she NEVER stayed the whole time my Sims were at work. My Sims were both in the Gaming career and I guess their workday ended after 4 o'clock or so but she always left before either of the parents came home and the kid was sent to daycare in the interrim. But always took her payment.
I did hire her on occasion in the city for Zoe and her live-in alien boyfriend. Mostly when the boyfriend just wanted to go outside onto the intersection to socialize (but wanted to keep the kid upstairs) but the price of the nanny wasn't worth it with only one parent working.