I have three. They're currently 4, almost 6, and 15 months.
My third has been by far the easiest kid I've had. He slept well from the get go, he nursed just fine, and he's very happy-go-lucky.
My middle boy has been our biggest challenge, as far as keeping up with him. He's very emotional, a terrible sleeper, and WILD. But he's also a total sweetheart, very intelligent, and super sweet to younger children.
My dd was the toughest as a baby--she was "colicky" or something as an infant, and I thought I'd never make it through her first year. Something in her switched when she hit toddlerhood, though, because all the sleep problems and crying evaporated.
I do think that three is hard as far as the workload, especially when they're all very small. The laundry, dishes, cleaning, etc., can be very overwhelming at times. It feels like a lot more than just the mess of one more person for some reason. But I've just had to adjust my expectations and do my best. I keep thinking that someday, I'll be able to have my house just how I want it. But for now, I need to be flexible. Of course my timeline has been pushed back again, as we're now expecting Baby #4!
IMO, the first baby is the HARDEST. Of course mine was just not an easy baby, but everything is new and there can be a lot of self-doubt if things aren't going well, and you don't have the perspective to know that it won't be just like this forever. I've also been told that having three is as hard as it gets, and if you can do three you can do any number. I'm hoping this is true, but I suppose I'll find out soon enough.