Bitcoin vs Ethereum. My 2cents.
I like focusing on Bitcoin and Ethereum because if you can wrap your nugget around these two blockchain technologies, then you can understand the essence of blockchain and cryptocurrency in its entirety. And the faster we get everybody up-to-speed on blockchain technology, the faster we can all stop using centralized solutions for our every-day wants & needs.
So firstly, what do these two blockchain technologies have in common? They both have their own blockchain with an independent network of developers and miners. They both have their own cryptocurrency---Bitcoin has Bitcoins (BTC) and Ethereum has Ether (ETH). And they're both the largest blockchains currently in existence right now (it's November 2017 right now, by the way). I say "right now" because I assure you, this could very well change one day.
They've also both experienced "forks" as a result of turbulence and/or "differences of opinion" amongst miners & developers. Ethereum's fork occurred a couple years ago after a group of investors put their money into a virtual blockchain pot (if you will) and were hacked (it was bad). Ethereum patched this up and forked off the hacked chain now known as Ethereum Classic, which is "still going" albeit not nearly as strong as Ethereum. Bitcoin, although never hacked, forked as a result of differences of opinion (resulting in Bitcoin Cash) but more recently ALMOST forked again when a herd of developers, investors decided that bigger blocks were necessary to increase transaction speed and lower fees for Bitcoin users (because what's the point of using crypto if it's slow and expensive?). However, this "Segwit2x" fork was "formally cancelled" due to the turbulence it was creating within the Bitcoin community .... and still creating.....
How are Bitcoin and Ethereum different? Well, for starters Bitcoin is the biggest, baddest blockchain out there with an insane amount of market cap (like, $130 BILLION) and an enormous network of miners while Ethereum follows in 2nd place with a respectable $31 billion dollar cap. Bitcoins, which are finite (meaning there is a limited amount of them) are worth some $8,000 per coin while the Ether hovers around $330 per coin. But could this just mean that Bitcoin's cryptocurrency is over-valued (maybe because there's a limited supply....kind of like gold)? The jury is still out on where Bitcoin's intrinsic value lies but the value of the actual technology is a whole 'nother ball game.
In this regard, Ethereum currently has more technological flexibility and could very well replace Bitcoin as the biggest, baddest blockchain on the....block. Why? Because they're developing tools that can be used to build products that are 1) Easy to use 2) Work well and 3) Are more easily adopted by mainstream consumers (like us, right?). Meanwhile, Bitcoin is still kind of flopping around trying to figure out how to fend off controversial forks in favor of maintaining their decentralized, secure status quo. This is not a bad thing, per se, except that it's all juuuuust a little volatile. Don't get me wrong, I love Bitcoin and they could definitely get their sh*t together and storm forward with something totally innovative, amazing, and useful; they have plenty of talent and support to do it, I'm just not seeing the "light at the end of the crypto tunnel" for them (I mean, aside from the whole $130 Billion dollar market cap thing).
Also, Ethereum was the first to introduce the idea of "Smart Contracts" which will one day (mark my words) replace the need for lawyers, banks, and (sometimes) over-reaching government regulation. Ethereum is also launching a mobile operating system for iOS and Android which means WE (you and I) will soon have things like mobile web browsers, messengers, and other cool stuff that runs completely on the (decentralized) Ethereum blockchain. This means sovereign global transactions, messaging, and communications, and more importantly, makes us (THE PEOPLE) the sole owners and stewards of our money and information!
THIS IS HUGE, PEOPLE. IT IS "THE WHY."
Imagine a world where individuals (not banks, governments or corporations) PRIVATELY decide how, when, and why we transact and communicate. This is as meaningful and revolutionary as the initial launch of the internet (but minus the centralization and creepy control over our information).