I disagree that BTC will always be King. It, sadly, really isn't that great of a coin where it stands now compared to many of the others available.

What BTC has going for it is a top following and plenty of money within the foundation to modify it for the future so it can at least compete up top.

As much as I hate to admit it, as I was wrong about it for years, Ripple has a great shot to be the King, and it's mainly due to transaction speeds, and marketing as well It, right now, is the only option available that big companies can adopt because they need a coin that can handle 700-1000 transactions per second on the big sales days.

My favorite coin at the moment is ZCash because of the options it has. It's very similar to BTC, almost identical, but for future standards it has possibly the best opportunity to be be adopted by the everyday user, but also has some nice perks that would allow it to be used by Government Agencies, The Healthcare Industry, and any other group that may require confidentiality. The fact you can choose between pubic and private transactions gives it a great sell to meet in the middle, so to speak, from us to the IRS.

All this being said, unless we all start hooking up windmills to our rigs and computers, the energy usage may not be sustainable long term. The foundations should be able to fix this overtime with implementations in the code, but it's just a matter of time before the Green Coins start coming along.