Are you using BitBTC or Open.BTC? I would say this, with that difference in percentages I would go to the bitUSD pair as soon as possible. It put it up twice the growth that bitBTC did today against BTS.

The other reason is to keep your money in a steady currency if you are making trades....or really for the long term as well. At time you may benefit more from the BTC pairing, but only while BTC value is rising.

The most prudent action IMO would be to take 75% of the funds, and go to BTS against the USD because it's gaining more currently and will retain more value even with the changes in BTC, and have 25% in BTC. It gives you more options, and chances of catching a big wave up in one or both instead of always feeling like you're on the wrong side of the pairings.