Yes, i think this is a right time to buy altcoins because at that market is down, when market rise after some time & this is a right time to earn good profit. I prefer ethereum is best coin for long term & short term also and it comes after Bitcoin & everybody like it very much.
You are right, the market is currently in a phase where it is very advisable to buy, and if you can have some Altcoins it would be very interesting since it is a way to diversify our bitcoin investment. At the moment that bitcoin begins its bullish stage, all the altcoins will follow them, it is not known when this phase will begin, it is best to buy and maintain, to have it as a long-term investment.