I'm pretty old school about my bicycle log book. It's a bound journal for bike maintenance, in which I make notes about replacing tires, chains, etc., with dates and odometer readings. Kind of similar to the log books I have for our cars -- date, mileage, how much gas/from where/price, or oil change, tires, etc.

I've got two parallel "logs" for rides. An Excel spreadsheet keeps track of ride lengths by date, and I make notes about each ride in an engagement calendar. This system works for me.

Note, if I were "training" on a training plan, I might want something more like average speed, intervals, training effect, etc., etc., ad nauseum. You can do a lot with a copier or printer and a hole punch.