I strongly prefer the term "lady(ies)." Occasionally, I may use "provider." Rarely I use "escort." When talking to a lady, I tend to use her name.
Some of the ladies prefer the term "courtesan," I assume due to the historical context of the term.
However, the term "hooker" has its basis in US history, and if you're relying on history, US history is more specific than the era of European courtesans.