For the moment, the bitcoin blockchain is the most 'used' and it is the most secure but like I said "for the moment". However it is normal that in the future someone will build something better than the actual bitcoin (this is obvious... technology).
Says who? You can't know this for a fact. As long as the developers actually do their jobs, there is no reason for Bitcoin to fall behind.
So far, we've seen almost no implementations in the altcoin world that deserve the attention of Bitcoin. Besides, when (if) *insert company/government agency* creates another coin it is going to violate one of the fundamental ideas of such peer-to-peer currencies, which is no central authority.
Update: Several corrections.
Currently we have the Internet. But one day we will use a different Internet... you know... innovation..