I don't believe Bitcoin will be the one and only and I think Ether has a lot of potential but they have different utilities.
Despite what people are saying Bitcoin has a HUGE advantage over other coins. The initial distribution.
Since the rise of Bitcoin that made many early investors a lot of money there has been a wave of new investors looking to get rich quick with other coins. Speculation is pushing the prices of these other coins past their actually value based on real world use.
I often compare it to the sports card bubble of the late 80's and 90's.
Before the 80's kids collected sports cards but did not know their actual future value. They would put them in the spokes of their bikes, glue them to a book, or store them in their wallet. Eventually parents threw them away, they were destroyed, or they were sold with the house they grew up in. When the 80's rolled around and the demand grew for these sports cards and people began cashing in on their childhood investments. The sports card craze had begun and all of a sudden everyone was collecting sports cards. They were kept fresh in their display cases, nothing was destroyed in hopes that someday they could also reap the rewards of the past. While this occurred companies like Topps, Upperdeck, Donruss, etc. over produced to keep up with demand. Now those cards are worth nothing because they were over produced and most still exist. Bitcoin is very similar. They were lost, destroyed, given away, etc. and when the value of Bitcoin blew up everyone wanted to jump on the train. Now, just like the sports card bubble, altcoins are being overproduced and overbought. Will we have the same conclusion?
If you are looking at BTC purely as a store of value, an asset, then you have a point.
But if you want a currency - to be able to buy and sell things with it, to use it to move money around the world - it's increasingly looking like BTC will fail at this because of the blocksize limits.