When you book a massage treatment then you may be able to choose between female massage therapists and male massage therapists. While some people will not mind being massaged by a member of the opposite sex, others won't feel so comfortable. Are you uncomfortable with one of them, and if so do you feel awkward voicing this? It is a thorny question.
So, how to choose from male and female massage therapists? Bear in mind professional therapists are fully trained in proper draping techniques so modesty is always protected, they always respect boundaries, and gender is not relevant to them.
Some men find it more pleasant and relaxing to be massaged by a female. Conversely some women will prefer to be massaged by a man as they have stronger hands and can often really get into knotty shoulders. Women can also feel judged when being massaged by another woman, while men might not feel comfortable being undressed in front of another man.
Massage therapists are professionals, but ultimately it is your choice as to who you feel comfortable booking. However choosing someone on the basis of their skills rather than gender could just mean you have the best massage of your life.