Actually there should be a "What to buy" section on this board, because this topic is really asked everyday 
As mentioned before, you should know which risk you want to take to gain your wished profit.
Many people said this before, but I it's true that there're a lot of promising projects atm and you should choose well in case of long-/mid- or shortterm and split your money on a couple of coins to minimize risk, but also increase chance to win although it's less
As mentioned before, you should know which risk you want to take to gain your wished profit.
- safest:
- Ether: I think will be the most profitable of the safe investments. Next Year with Proof of Stake it will bring a lot of investors
- LTC: really safe investment and will get more and more value over time and might even get a really big rise at some point
- BTC: I know, no altcoin, but still pretty safe investment for longterm although it's not that profitable anymore
- little bit more risky, but good profits:
- OmiseGo: absolutely great technology, with famous people in the team, a promising future and a lot of followers
- IOTA: great concept that and if more famous exchanges accept it, the price will go up pretty well.
- Lisk: good team with a good future
- Waves: honestly don't know much about it, but a lot of people are believing in this, so there're already a lot of followers
- EOS: still in the starting phase, but seems to be great and already getting all the time a big rise whic could maybe go next year up to 50$
- risky, but could get a lot of profit (I actually mostly avoid those coins as I prefer the safer way)
- Neo: depending on the news of China it could get really high, because China brings a lot of really big Investors (also still holding a few of them)
- Stellar Lumens: still really cheap and already rising well
- Einsteinium: This one you should buy now, because there's a hard fork comming in 7 days (timer and infos https://www.emc2.foundation/). This Hard Fork also includes a coin burning which will reduce the coin supply by 50 Mio. coins and will make the price go up for sure (happened to every coin who did this before AFAIK)
- Other coins to inform about that look like a lot of potential for next year (and also already had):
- Qtum
- Ark
- Stratis
- SALT
- Golem
- Status
- Shift
Many people said this before, but I it's true that there're a lot of promising projects atm and you should choose well in case of long-/mid- or shortterm and split your money on a couple of coins to minimize risk, but also increase chance to win although it's less