Of the two, I'd say you'll get more general use out Tots, but only slightly. This is especially true if you're going to get the Lilith box as you said. She'd be a 3rd master to factor in, and she will usually do better with Tots as well.
That said, if you are more likely to play The Dreamer often, get the madness for all the reasons people have said above. Basically, The Dreamer wants his own crew, while nearly every other master picks from around the faction. There is certainly overlap, but I've bought more models (mostly) just for The Dreamer than any other master I have.
Edit: basically, get both.