If we talk about short distance - i buy some Ethereum Classic and will hold it till march

your preferences are fine, mate. I would add a litecoin to the list, because very large rumors began to spread.

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3 good altcoins to invest in for large returns over 3-6 months?

I think you need to look at the recent popular ICOs that were sold out in presale, and then try to buy the coins at near ICO price on a DEX such as IDEX where coins are available as soon as they are released. By the time coins hit bigger exchanges such as Binance or KuCoin they are often already up 10x. I was able to do this on IDEX recently, buying good amounts of 3 very promising altcoins at prices near ICO - Origin Trail (TRAC), Stack (STK) and Devery (EVE). I expect these coins to be listed on big central exchanges and to be up 10-25x or more in 3-6 months! I’m waiting at present to buy WanChain (WAN) on IDEX once the sale tokens are exchanged for the tradable tokens.

CAPP and IXT are long-term tokens that can be aimed 30-50 times
Both are promoting business with famous enterprises (Genre Nvidia), the development is also smooth, there are also points that are not blessed with exchanges.

These tokens are leaving the most wide range.
Easy to realize business because development is going well
Since the target market is big, the ceiling of market capitalization is high
It jumps up every time it lists with overseas medium-sized exchanges, major overseas exchanges, domestic exchanges

My investment is only at ETH right now. I want to diversify my portfolio too but not seeing much in the market. No lending coins, other smart contract coins look a bit tempting but still too immature.

I never heard about YOYOW but i'd be interested to know more about that crypto, if someone can give us some infos..
WAVES is very cheap now, very high potential, time to buy... just like STRATIS !

i think ETH, NEO, and RIPPLE have a good development for 3-6 months forward.

I advise you to invest in ETH and RIPPLE. ETH can be used for long-term investments, while RIPPLE can be for long-term investments or short-term investments.

Yes, these coins have a good growth potential for the next half year. But I do not really like ripple. Yes, it's a good coin, yes, it will grow, but I do not like it. It's my personal opinion.