HMC my dd2, 4 next week, is still the hardest, always has been and probably always will be. very interactive doesn't like sitting still and quietly.
it's the quantity really. like on flights, we have me with one child and dp with two, or vice versa. no break for us at all, unless you count having *only" one in your charge for a while. it's wearing. and, if two are sleeping well, the 3rd will be ill, or teething, or having a nightmare. so even if all 3 sleep through the night most of the time (as mine do) you still get a fair number of broken nights, even if each child only wakes once or twice in a week, that can be 4 or 5 broken nights in that week for us.
term time is better. we have a nice routine, lots of childcare. time off for the grownups. etc. don't I sound middle aged and boring there? (and we weren't once, honest... we were really intersting and dynamic once.....)