I’d invest in NagriCoin

I don't think $50 can be called an investment, if anything, I would call it playing the lottery or playing scratch and win.

If you really want to achieve something important, commit an important amount, but above all commit yourself and your time to study the crypto world (maybe invest the $50 to do that).

Even if only due to all amounts of money, simply do not waste time understanding where to invest them. Go out to eat something with your girlfriend, that you'll see are better investment !

I'd try to find a post ICO coin that has just been sold off massively but still holds long term promise. There are plenty of people who play the ICO and flip game and that always leaves some good deals out there.

Actually it does not matter what amount of money do you have to invest.
First of all you have to minimise your risks, so It is better to divide your portfolio on groups such as:
Bitcoin - 20-30%
ETH,LTC,NEO,Monero, Dash - 20-30%
Iota, EOS, Waves - 10-20%
More risky: TRON, Verge etc. - 10-20%
ICO - 10-20%

Anyway you have to make an analysis of the market in order to pretend on profit.

I had this initial sum, I have enclosed him in XEM, I in minus now, but I think my situation eventually to be improved

If I would invest 50$, then I would invest in a risky altcoin or even put it an ICO. If you would loose the money, it will not hurt as much as an investment of 500 dollars or more.

$50 is too small for investment. But If you want to feel the profit make it atleast $1000. If I had only $50 I would invest in one coin and that is Bitcoin and then trade it. Trading with patiently so you can turn that amount of money in to 10 times a few month.

I'd invest in new coin only if it has smartcontracts because it's the feature

I think 50 dollars is too small. You will not gain much in a small period of time in that amount of money. You will wait for years before you gain a huge amount of money. Less money equals less risk. But less money equals less income. Why do not you make it bigger? There are a lot of cryptocurrencies showing us a wonderful rate of change in their prices.