Yes, you are right December and January months makes me feel unsure too. Actually, there are some time cycles and trend cycles movement takes place during these two months. Now coming to the point these three coins XRP, XLM, TRX  are ok to invest for both short-term and long-term, but for now, you can choose coin like Neo, Litecoin, Ripple and Monero which are already doing well both trend wise and Strength wise as I have already started investing for long-term in these coins.