At the moment literally, none of them is a threat to Bitcoin. And as it seems none will be. Most of them will disappear sooner or later.
Yeah most of them might disappear but the thing is there are some backed by very reputed companies in the global trading industry so son't you think that will be an advantage for other currencies over bitcoin and unlike nine years ago we have to admit that today software development methods are much advanced and with that can some of alternative currencies grasp the business market because of there technological advancement and the benefits they can provide for there users with it