On crypto world its nothing 100% safe. You dont have to be afraid about not being 100% safe because nothing in this world are 100% safe. We can be 100% sure only for taxes and death 
Anyway in my opinion the most safe coins that also have a good potential to double or tripple your investment in 2018 are :
1.Bitcoin
2.Ethereum
Some other coins that you may benefit but i consider them less safe than the first 2 are :
1. Litecoin
2. Monero
3. Neo
Last but not least are some coins with very cheap value ( these are the most risky investments because if they don't deliver their project how they pretend the coin can be dumped and you can lose everything, but if they manage to deliver their project and continue following the steps on their road-map can give you huge profits)
1. SONM
2. Golem
3. Siacoin
4. Einsteineum
5. Flixxo
The last one is based on my intuit : Digibyte (Some of you maybe will laugh or will criticize me telling me that they have near 10billion supply and max supply 21 billions) i picked this coin because the coin itself its very well organized, i have experienced always the fastest transactions (almost instantly the coins are transferred) and also the transaction fee is very very low ( almost zero $ ) In the future the interest on this coin will raise, people in the end will ask more fast transaction and less fees.
Good luck with your investments !
Anyway in my opinion the most safe coins that also have a good potential to double or tripple your investment in 2018 are :1.Bitcoin
2.Ethereum
Some other coins that you may benefit but i consider them less safe than the first 2 are :
1. Litecoin
2. Monero
3. Neo
Last but not least are some coins with very cheap value ( these are the most risky investments because if they don't deliver their project how they pretend the coin can be dumped and you can lose everything, but if they manage to deliver their project and continue following the steps on their road-map can give you huge profits)
1. SONM
2. Golem
3. Siacoin
4. Einsteineum
5. Flixxo
The last one is based on my intuit : Digibyte (Some of you maybe will laugh or will criticize me telling me that they have near 10billion supply and max supply 21 billions) i picked this coin because the coin itself its very well organized, i have experienced always the fastest transactions (almost instantly the coins are transferred) and also the transaction fee is very very low ( almost zero $ ) In the future the interest on this coin will raise, people in the end will ask more fast transaction and less fees.
Good luck with your investments !