Number. If I glance twice just a couple minutes apart, I know there's an unusual drain going on and know to look for problem apps/processes I forgot to disable when done with them.

Also the number just feels like more direct communication to me than a graphic and is easier to make choices with. It's not quite the same thing, but when I look at a clock I don't want to see "5:30ish", I want to know if its 5:28 or later so I can start my end of workday process.

So, number because spectrum.