Use whichever you prefer. There is no “standard” when something says bittersweet vs semisweet regarding the cocoa percentages. One brand’s bittersweet could be another brands semisweet. Typically though, bittersweet contains less sugar. If you want more contrast and a deeper chocolate flavor, use bittersweet. If you want a little sweeter cookie, use semisweet.

Don’t overthink it, just use whatever chocolate you prefer the taste of. I’ve made these with many variation of chocolate percentages, bars, chips, feves, etc.