This is exactly what I have struggled with the last year or so. I think a combination of both is best. I think it also depends on what you are training for, your age and ability to recover.
I have done Crossfit the last three years and really enjoy those types of workouts and the competition involved. I would consider myself in good shape, especially for my age, I'm 42. I have maxed out at 365 on back squats and 405 on dead lift. I weigh 180.
The problem with Crossfit is the a ability to recover and play tennis at your peak ability. At least for me. I did band workouts for 2-3 months and had tremendous success with them and was able to recover quicker and faster. We would do HIIT training with the bands similar to Crossfit. We would also mix in sprints with the different exercises.
If you are just trying to build strength then I don't think there is a question on what's better for that- free-weights.
If you are trying to train for tennis and the physical/cardio demands involved I think a combination of free-weights, bands, and HIIT training might be best. Maybe free weights for just strength training and bands combined with HIIT training to help with tennis conditioning and recovery.