Well man Ill recommend you try trading. Buy some altcoins at low value and sell it high. That way you can make 17BTC or more out of 7 BTC just don't use it to buy only 1 altcoin spread it. Grin
Trading is a good way to earn money but also to lose money, which is why you should first invest time in the altcoin you want to buy and speculate on. There are some indicators of coins which are good or not good:
- steady updates from the devs.
- a roadmap
- developers who aren't hiding
- an active community