whats the best currency to invest?

The most important thing to mention is, that wether its BTC or LTC or or or you should only invest money which you can afford loosing. The investment in cryptocurrencies is highly speculative.
Maybe the investment into a "mining group" is another option instead just buying coins and hoping their value will raise. Especially BTC is overvalued in my opinion. And that said, many other currencies are
connected to the value of BTC making it a rollercoaster.