Here are the differences:
Dash: scam. Instamined, claims to be anonymous but isn't, spends buckets of money on marketing instead of letting the code speak.
Eth: Started out good. It's a turing complete cryptocontract platform, which basically means anything you can build in code (including other cryptocurrencies) can be build on ethereum. The problem is that development is very centralized, they are being guided by huge organizations instead of grassroots users. Price will probably keep going up for a while but I would actually put money into ETC instead of ETH because it's far more decentralized (in terms of development and direction) which means it stands a chance of becoming very very big (compare the "Internet" to "Microsoft Network").
BTC is losing market share right now as people look towards altcoins, it's typical gartner hype cycle situation - the prices will go up, then the vast majority of them will go to 0, but some will survive the culling and prove to be useful for some of the things they are claiming right now. BTC has already proven itself (in this regard), so when all these altcoins start heading to the floor BTC will be a safehaven.
That's my opinion anyway.
Eth development is least centralized. Many node implementations exist in various languages with a steog foundation and vitalik driving development.
Btc has steongest brand recognition and market cap and very stable proce appreciation reative to other coins in past 2 years.
Dash has unique and valuable consensus and governance mechanism.
My 2 cents summary... (since I also had to make a decision on this today)
ETH also
appears it will end up having the first secure instant off chain transactions system (although realistically via centralized hubs).
BTC is failing into
paralysis and self-destruction, which is tarnishing its former flagship image.
DASH is
a fool's pyramid pump scheme.
Monero (XMR) doesn't have instant transaction scaling so I can't put it in the same league as the others. @AnonyMity (and privacy) is a feature every serious ecosystem can offer as an option so IMO it isn't sufficient as a sole selling point. Monero has a self-adjusting block size algorithm (but I've argued all PoW systems are subject to the same centralization effect as they scale regardless), but adoption is about scaling and ecosystem applications. Monero might be a good diversification, but speaking for myself as currently a risk adverse speculator, the chart isn't the same as BTC, ETH, and DASH so there might be something else going on there (although one could argue it is same or exaggerated first hump due to BTC millionaire @rpietila shilling it in 2014). Not sure. Ditto Byteball's chart doesn't give me enough confidence to bet big on it (and also know it has major technical flaws such as the transaction fee design and the witness replacement mechanism), although for speculators who want more risk they might consider it.
Thus
I've diversified into ETH (
with BTC that technically isn't even mine as it was given to me by my angel investor). Best of the worst. Except I do agree that Ethereum has more app-specific (aka smart contract) ecosystem development than any other.
Bitcoin:
is decentralized, it has a lot of adoption, it has a lot of users, a lot of usage, a lot of real world applications and a lot of services that you can pay for with bitcoin. the distribution is the best, there has never been any premine or any bullshit to get the coins, you could get them from day 1 if you wanted and there is still no restriction, you can buy or if you are willing you can invest and mine it.
the market is the biggest and that means speculation on it is a lot easier than any smaller markets.
there is real adoption where new people come and buy bitcoin because they either want an excellent investment or they want to use this cryptocurrency online as it is intended to (a peer to peer decentralized digital cash).
and a lot more.
Dash:
it has a decent amount of supply and that can help its inflation and finally the price. it is a pump coin and that is a good thing for making a big and quick profit.
it has a big premine. and many even call it a scam. it doesn't have a positive public face. there really isn't any real world usage for it.
in the anonymity department it is not really anonymous. and compared to other coins it has nothing to say compared to coins like Monero.
there is no adoption, only traders switching their money over to Dash and out of it after they are done.
it is a pump coin and that is bad because it kills the coin in the long term when it is pump and dumped.
ETH:
it had a good idea at first but it is implemented pretty badly.
the code is bad and has many bugs, many of which has already been found. some of them even exploited and one of them led to a hard fork and splitting of ETH/ETC and there will always be a possibility of the same exploits and other unknown bugs that can be devastating to anybody who has his money in this coin.
it has a big premine (in form of ICO).
there is no real world usage for it and the smart contract that they are so proud of is not really something special on this platform.
the supply is HUGE. it has one of the biggest number of coins available and with a simple supply and demand rule the price will always be under constant sell pressure.
there has not been a clear cap on the maximum number of coins available.
the last and the worst but not the least is the centralization. this coin is one of the coins that is completely centralized and everything from the price to the code and the future is being decided by those who control it and can easily be manipulated to their advantage.
I agree about Bitcoin except Bitcoin is putting that #1 position in great danger by mucking around with HFs such as the technologically myopic Bitcoin Unlimited.
I agree on Dash.
I agree the possibility of hacks in Ethereum is great, but I am not diversifying into it long-term. I'll be back out of it again when I see the next YUGE smart contract which a hacker can target. I think Ethereum's community will be much more diligent about not letting such a concentrated accumulation occur again at this nascent stage of the new pump that is just getting under way (as it passed its ATH recently).
The real world use is that is a massive experimentation platform for figuring out which applications of blockchains might be worthwhile. And a speculators ICO paradise. Massive amount of smart contract ICO app activity kicking in now. ETH is the next hot thing coming as Dash's pump gets nearer to its apex.
BTC is undergoing turbulence and I think ETH will step on accelerator for the next month or two at least, while BTC and BTU slug it out. ETH and ETC already had their war and Vitalik won.