I'd say mirror and lift progression, but I think it's really a combo of things those two being the most prevalent. I'm old and just trying to be as fit and strong as I can possibly be. Great question II!
Like bybon said, it's mirror+scale for me. On an anabolic cycle I will pull out the tape measure and bf caliper to make sure I'm doing everything to better my investment.
I log bodyweight along with weight lifted on a daily basis but I don't compare it but once every few months maybe. It only takes 1 minute out of my day so why not...
I said lift progression because that's what motivates me. When my lifts go up, I get more pumped to do more and more... I also use the mirror as an indicator. If I like what i see, and I'm happy with results in the mirror, i'm happy
Only care about lift numbers right now. When cutting down bodyfat I think the mirror is the most useful. Everyday in the morning when shaving I take off my shirt and see where I'm at. I was completely unconcerned with bodyfat for about a month but now I think I'm leaning towards trimming a little.
I put other because I use them all with no particular one more than the others..they have different purposes for each in the day to day or overallgoals
mirror. the scale will lie to you.
for example, my second cycle i only gained 10 lbs on the scale but my arms and neck were an inch bigger and my waist was smaller.
the tape measure is a close second
I go for various measures of athletic progress, how quick I'm getting the routine done, how much volume I'm using at a given point in my training, recovery time.