$ 2000 should invest in XRP now, because this coin has a chance to rise in December 2018, as this coin is currently in second place and may grow at the end of the year. now on.
What chance? Why are you believing in a growth of xrp in december? There are nor fundamental nor technical prerequisites to rise for this "crypto".
Every coin have some chances to rise next month, more or less. Why would anyone invest all money in one coin, why in xrp, just cause you think it will grow, without any other arguments? For every coin we can say the same, with 2,000$ I would diversify, some in btc, some in eth, some in xrp, stellar, eos, there are many good coins that have a good chances to rise in future, maybe not next month, but they will one day, nobody can claim when exactly.