Last couple years WKO, but before that I had a weekly planner where I wrote things. I'd sum hours each week and write that down on each corner (one week was a left and right page). In the old days I summed miles, but I think that's not a good indicator of training anymore, esp since I ride on the trainer most of the time.
Small enough that I'd write only critical stuff, big enough that I could write critical stuff. I've tried daily planners but they get bulky, and I don't feel like writing in them. Small weekly planners are too small. I like the 5x8 side or whatever is the size in that range.
I have almost all my journals from 82 or 83 on. It's interesting to see what I did here and there. And what I thought was critical back then.
I don't train too scientifically though. I do mostly just pedaling, I try and break milemarks (20 min avg watt, max watt, max speed), see how long it takes to do a loop if I feel like it, and race.
cdr