I'll re-post this from July as my answer to OP:
...It should be somewhat clear that 99% of existing alts will lose 99% of their value over the next few years. Most alt "innovations" either aren't innovations (like tweaking blocktime or supply), don't work, don't scale, or don't matter. Furthermore, ninja-mining, pre-mining, ugly emission curves, 51%s, NaS attacks, etc, can all kill coins even if there *were* actual innovation. And further still, it's probably the case that if any meaningful, viable innovation ever gets done in the alt-space, bitcoin could eventually incorporate it, making the separate chain irrelevant.
You have to understand that bitcoin's innovation was 30yrs in the making. Solving distributed global consensus was a breakthrough in computer science. There has not been a single innovation in the alt space that even sorta compares to that. Not one. Which is why bitcoin is highly likely to remain dominant.
Furthermore, it's been well understood for the past 20-30yrs that if you could solve distributed global consensus, you could do digital cash, and it would be a big deal. It's just that no one had figured out how to solve double-spending (global consensus) prior to Satoshi. There is no similar known problem being attacked in the alt-space for which a solution would be a breakthrough of similar magnitude. So an alt would have to luckbox into some completely unforeseen yet incredible innovation.
So bitcoin likely remains the primary crypto-coin. That said, there *are* potential niches to be filled by alt-coins. The only one I can clearly identify is anonymity. It's clear that bitcoin does not offer meaningful anonymity unless the user is technically skilled enough and motivated enough to obfuscate their transaction chains sufficiently. Furthermore, bitcoin is becoming a global asset class, fit for corporate balance sheets and HNW portfolios. It's also obviously seeing high-profile merchant adoption, and tacit acceptance/approval by various governments and regulatory bodies. If bitcoin offered technically pure anonymity that required zero user effort, governments would probably be a lot more directly hostile towards it. Thus, it seems unlikely that the bitcoin community would embrace full-anon tech in bitcoin core; lest governments react harshly and reduce existing ecosystem investment value dramatically.
So that leaves the anonymity niche open to an alt. As I've previously noted, ever since Zerocoin was published, I thought that when it came out as a functional implementation, it'd be the first actually interesting alt-coin. Well, it looks like these CryptoNote coins have beaten it to the punch of functional anonymity. Which CN coin will win is a different matter. XMR seems out in front, but the waters are muddy still.
I don't see any other obvious niches for alts. Turing completeness is interesting in theory, but I wouldn't trust the security of such a chain for a quite a while, and much of the benefits may be possible in bitcoin anyway. Other than that.... ?
Now that's not to say you couldn't make a killing if you play the alt market perfectly, and jump from coin to coin as they fall in and out of favor. But good luck not losing your shirt.
tl;dr: Alts suck, with very few even theoretical exceptions.