Newborn? Toddler? 2's? 3's?

I feel like whatever stage I'm in is the hardest!!! The first time around having a newborn was SO hard, but the second time it wansn't so bad afterall. Now DD1 is 3(!) and she's the best/worst person ever. I'd say the 3's are hardest. Or maybe it's just first borns that are the hardest?