I haven't looked at this in a while, but for USD to Alt here's the fee you're looking at.
BTC: GDAX BTC Purchase Exchange Fee + GDAX BTC Withdrawl Fee
ETH: GDAX ETH Purchase Exchange Fee + GDAX ETH Withdrawl Fee + (Whatever the market spread is between ETH or BTC for the alt you're going to buy)
You can also LTC if you feel the need to go fast, in which case it's
GDAX LTC Purchase Exchange Fee + GDAX LTC Withdrawl Fee + Binance LTC to BTC Spread + Exchange Fee.
Look up what these numbers are and you'll see what's cheapest.
BTC: GDAX BTC Purchase Exchange Fee + GDAX BTC Withdrawl Fee
ETH: GDAX ETH Purchase Exchange Fee + GDAX ETH Withdrawl Fee + (Whatever the market spread is between ETH or BTC for the alt you're going to buy)
You can also LTC if you feel the need to go fast, in which case it's
GDAX LTC Purchase Exchange Fee + GDAX LTC Withdrawl Fee + Binance LTC to BTC Spread + Exchange Fee.
Look up what these numbers are and you'll see what's cheapest.