I would suggest PROXY and Logarithm.

In my opinion beside ETH, others altcoin that have big potential and good in fundamental is Power Ledger and SALT. The purpose of these 2 project is really interesting and give many advantages to the customer,  investor and token holder.

Top 2 for now is eth and btc. These 2 coins will definitely give you profit in 3-6 months.

The topic of this discussion sounds like you want to put money into an altcoin NOW, as in today or tomorrow, but you mention the next 3 to 6 months?
Does that mean you want to buy a coin now that will moon in 3 to 6 months?

If you are looking to put money in an altcoin now, I would recommend:
DON'T DO IT!

Isn't it obvious that most coins are in a bull run right now and prices are inflated?
One of the biggest rookie mistakes is to see the markets rising and wanting to get in on it and buying a coin at a high price.
Look at the long term market trends, there is always a dip in price in BTC every 2 or three months and when that happens the prices of altcoins crash too.

Instead, watch which coins perform well, then which of those have upcoming development, then when it's price crashes buy it.
Then 5 to 6 months down the road you will get much higher returns

My choice would be playkey and ins, not only i am using it right now but what i like about this icos are that they are very promising ico and they are a successful one that is why it is very safe to invest in these two icos right now, just trust the process and believe i am sure it will be worth it.

OP have you looked at ucoin too. I read they are getting to the market this month, they still on ico and a little difficult to get in.
LTC too is a futuristic coin. Best of luck.

if i have to choose 2 altcoin right now, i would pick lisk & lumen, both has great team and 2018 will be great for both coin.

Monero and Dash for me

i see FAR too many people investing in Ripple. Ripple is the banks coin, ie.. very centralized. The bankers are thieves, and I expect mass bank failures soon in the future. When the banks start to fail, because they are NO LONGER NEEDED with cryptos on the scene, they will look for any liquidity they can garner. They will quickly liquidate all Ripple coins they hold to try to maintain their scams.....

My warning, stay far, far away from the thieving bankers coin

I believe these are:

1. Ethereum. It will grow like mad sh*t in 2018

2. Raiden, cause it will fasten ETH transactions. And it would be very interesting.