I like silent updates when they're not likely to be huge user-visible improvements, mostly performance enhancements and bug fixes. In the case of Firefox or Chrome, for example, I'm perfectly happy with the current feature set and just want them to keep getting faster and more stable. On the other hand, most of the Android apps I use are missing a couple of functions or have some annoying visisble bug I am waiting to be fixed. Then I prefer updates to be automatic but not silent so I can read the change list and if something I am waiting for has been added or fixed I know (and rejoice) right away.