I think one of your considerations should be how do you listen?
Meaning... if you opt for something like Al K's extreme slope crossovers (which I had), you can probably get more volume out of your speakers and keep them sounding better because of the smaller overlap between the drivers.
On the other hand, if you are one who listens at nice background levels so you don't wake the sleeping children upstairs and never shake the walls, then perhaps some of the more simple crossovers would fit since they might allow the sound to blend together (because of more overlap) quicker.
I'm not an expert on this stuff...this is my simpleton understanding of the basic difference.
I will say this... I was part of a crowd that was at the Klipsch engineering facility once prior to one of their corp. gatherings and were treated to some 'experiments'. One of the things we did was compare something like a 12db slope crossover to somethign like a 24 (or was it 48 db?) slope.
It was pretty clear that the steeper the crossover the more clarity was in the sound. It was the first time in my life that I ever wanted to use (and finally understand the use of) the phrase "it was like a veil was lifted from the vocals"
In fairness, I don't know that I could walk into a room and tell you which slope was being used but side by side? It was pretty evident....steeper slopes rule.