Contract traders are also the same as the normal way of trading in my view. With contract trading a contract is made between the trader and the exchange which means if the prediction goes right he'll be profited and this is a kind of gamble with the price variation of bitcoin. With common form of trading instead of a contract the trade is set to be executed when specific value is reached.
This means that they just invested the same way as it goes with the generic way of investment or trading. In this regard, I don't see the best out of speculation using contract trading, because you could possible obtain what you could have in the standard way so why to ask for other options? Would it be just make things worse and complicated? Unless the profit that you could get will be comparably higher that the usual ROI. But it is still depends on a person on how he/she will utilize his/her investment to gain more.