You have some great answers to this question! There are just so many limitations to the words “best” and “better” that there is no right or wrong answer here.
For general fitness, I would have to say that BOSU is the simplest and most realistic way to go. I’ve used a BOSU apparatus with all of my clients at one point or another, and I have yet to meet a client who didn’t fully enjoy the stability challenge.
I think the use of the TRX/BOSU is a great tool to implement for most clients, depending on their fitness level. TRX & BOSU exercises can be easily regressed or progressed.
The TRX is great to use because you can change the intensity of most exercises by changing the foot stance/leverage of the exercise, and performing exercises on the TRX helps engage the core and shoulder stability depending on the type of exercise. Also, you can perform tons of exercise for the entire body using the TRX and it can be used in limited space.
The BOSU is great as well. You can take your basic squat, push up and most exercises and perform it on the BOSU, adding to the intensity of the exercises. There are also BOSU specific exercises that can be used for both athletes and regular population. The BOSU doesn’t take up much space and helps with balance, coordination, and stabilization.