There is no choice to be made. It's the tax laws that dictate which is used and Turbotax follows the tax laws. first short-term gains and losses are netted as are long-term. if one type is gains and the other type losses, they are netted and if the result is net losses whichever category produces the net losses is used. if both categories are net losses short-term are used first.
To complicate things a little the nets are after any election to carryback section 1256 losses (regulated futures contract losses if they exist) .
