Both of the advisors I am considering have a lot of experience - they both are full professors with at least 10 years post-PhD experience. The more experienced one has about eight years on the other, though, and I looked at that extra eight years as a measure of the size of their networks, and, indeed, it seemed to correlate with their students' end placements and performance. So, neither is 'young' but both seem to still have passion for their field and had current students who said they felt supported and attended to. In the end, the bulk of my decision is coming down to my judgments about their research programs - their cohesiveness, fit with my interests, use of interesting methods with a lot of room to grow, etc. - and the results of previous students because everything else was so evenly matched. Take this advice with a grain of salt, though: I might end up regretting my choice... we'll see!