Honest question: why is this ("density") an attractive attribute?
I completely understand the attraction to commutable schedules, as well as having schedules which both maximize pay and time off simultaneously. However, "density" implies a lot of work in a short period of time.
Personally, I want to do as little as possible for as much pay as possible in a given unit of time. I want to maximize my credit-hour density, and not my actual work density. In other words, let's say we're talking about a 5-day stretch that is worth 35 hours of pay. Credit being equal between the two, I'd rather do four (or three!) flights with three long layovers in that 5-day stretch than 4 legs per day with 4 short layovers.
My point is, "density" of work in and of itself isn't a measure of how to maximize the combination of pay and time off simultaneously. System form, trip rigs, min guarantees, etc, are what really determine this over the simple math of how many legs per day you're completing.