I think right now because Steem Dollars are worth more than Steem, it is better to take rewards in 50/50. Then if you want to change those earned Steem Dollars to Steem and power them up, go on the market and use your Steem Dollars to buy Steem and power it up. With current prices I think this ends up with a better result. But the situation can reverse if Steem was higher value than Steem Dollars. Some smart person please correct me if I'm wrong on this.