bitcoin has a good rate lately, if you believe bitcoin will continue to increase, try to buy more bitcoin. If you want your assets to be in a comfort zone, you can convert to usdt, the point depends on how well your strategy is to become more active in the market. what I see is that the market is indeed in a state of passion.
Not only bitcoin but other cryptocurrency also increase this week. If op want to get profit, you should convert all your coins into bitcoin or other crypto.
I think it's not too late right now, invest right now, you can get profit later. If you convert to USD, you will not get profit but at least your funds value is not decrease.
It also depends on the currency you are going to convert and the crypto market situation in 2019. If you choose Bitcoin, you can earn a lot, but you take risks to lose in case the market decides to fall again.