Bitcoin, no doubt! Don't miss the train, with the trend situation recently, bitcoin has been more stable, even nowadays the price go up, there are possibility to up again.
Altcoin mostly vulnerable to pump and dump (manipulated), there's groups who do that things. That's makes hard to predict where the trend move, if you join these groups also that's not guaranteed if you can earn profit, mostly they use false alarm which only makes a profit for them.
Yes, now it's time to buy Bitcoins, buy it fast and you will make a nice profit in some days or weeks. The price is increasing a lot every day. However it's not guaranteed to have the BTCs price for a long time near to $900, the price can decrease a little, so, if you want fast profit buy it now, sell soon, or if you have patience, hold it for more time and wait until BTC hits $1000.
To buy alt-coins it's better to wait some time, because now everyone is around BTCs, very risk to buy alt-coins now. I would buy an alt-coin only if I want to support it and give some help to the coin team, without thinking about real profits.