I keep everything in a spreadsheet. Works for me. I have columns for a description, number of figures, manufacturer (if known), link to a photograph if I have one, and some notes for use in games or painting. What I do not keep track of is game-specific information. Several years from now rulesets will have rotated out and others in, but the miniatures will still be there.
I’ll probably end up with something like this. If nothing else, keeping it simple is a good thing. I’ll probably keep wondering about ways to make it better, but if I can keep that urge in check I should be OK 😉
Right now, my collection is pretty small. About 10-15 years ago I decided I wasn’t going to be wargaming any more, and gave everything away. Last year I finally accepted that I’d made a big mistake 🙁 So, if I’m going to do it, now is the best time, before my collection grows much more.