I hang around on LinkedIN. With Google+ in its invite-only "field trial" stage and people writing blog posts raving about it, LI's Questions have been inundated (or maybe people just aren't reading before posting, how unusual) with "Is Google+ a Facebook killer?" style questions.
Same question all over teh interwebz by anyone who cares to write a blog post about it.
Other similar ones that pop up are "Is [this shiny new Blackberry|Android thing] an iPhone killer"?
It's kind of a stupid viewpoint to take. Unless of course you're a marketer and you're desperately trying to make people believe that THERE CAN BE ONLY ONE and your thing is it.
No.
The reason there's a hundred billion products on the line doing more or less the same things is because...wait for it...different people have different requirements from their toys. If everyone wanted the same thing, there would be only one. So it's not a case of is [this] a [that] killer. It's a case of does this do what I want and will it continue to do what I want in the foreseeable future without me having to "upgrade" my phone/slate/laptop/desktop next year, and does it aesthetically appeal to my sensibilities. Checking up what the company's morals and ethics are like is also good, but I think they're all borgs.
Same deal with the social networks. Seriously who gives a flying if G+ can "kill" Facebook or Twitter. Actually read their privacy policies and terms of services (they're unnecessarily long winded and the all caps at the bottom is annoying but they are not otherwise that scary or hard to understand), decide whether you agree or not, and jump on the one you like the best and convince your friends to get accounts. Or get accounts where everyone else is (unless you don't agree with the privacy policy or terms of service, in which case unless your friends compromise you miss them or they miss you). Hell if you don't care and have the time or the inclination sign up for all of them. The only one I know of that is completely decentralised and not-a-borg is Diaspora, which is still in alpha.
It's not a case of a product being "the best". It's whether or not it's "the best" for your requirements.
And on a marginally related note, use the search bar before blatting questions at forums or forum-like things.