#3 was easy here! (well, relatively
0-1 was hard, 1-2 was hard (they are almost exactly 2 years apart - I had trouble with having only a newborn and a spirited toddler). Dh was also getting his MBA at night during all this, which made him scarce.
#3 is 3.5 years younger than #2, and she just slipped into family life so much easier. It was great having someone to fetch a diaper or something so everything wasn't *totally* on me.
#4 was pretty much the same although she is close in age to #3 so it was back to having a newborn and toddler - this time the difference was I had a 7 and 5 year old to help a little, and they could be somewhat self sufficient in playing, etc. #3 and 4 are both horrible sleepers though (getting better...slooooowly) so that has been hard. I am "nasty mommy" when I don't get any sleep, esp. when pg.
#5 is due soon, I am hoping for an easy baby! A sleeper!
I think it really all depends on the age differences and personalities of the kids. That and what other things are going on in your life - like dh going back to school, family crises, etc.