The best way to choose a mala is from your heart and the quickest way to get there is to focus on the breath. Take a few slow and deep breaths in and out and calm the mind. Once you feel the shift in your energy, begin to look at each mala (if you are in person, be sure to touch them and try them on!). Believe it or not there will be a mala that will call to you if you quiet the mind enough to listen. Each time you go to look at another mala, it will draw your attention back to it. It may not be the mala you would "choose" or even the colours that you normally pick, but the stones will activate something within to let you know.
If this process isn't clear for you, muscle testing is also a great way to choose a mala. There are a few different ways to do this, and I'll illustrate my favourite ways; you can put one arm out straight in front of you and and ask yourself a 'yes' or 'no' questions such as, "Is my name _______" try telling the truth first and then lie about your name. Press on the arm with the opposite hand, the body will become weak in the presence of a non-truth. Then you could ask yourself if a certain mala is for you, and see if you test positive (strong arm) or negative (weak arm).
Another way to test is to close your eyes and ask your body to show you a YES. Repeat the word yes as many times as needed until the body 'lights up' and gives you a response in a designated area in the body. Then ask the body to show you a maybe, and repeat the process, and then lastly a NO. Then look at or touch the mala and ask if it's a YES or a NO and see which part of the body lights up. If you get a MAYBE, ask more questions!
Lastly, you can pay close attention to the subtle energy within the body. Notice if you expand when holding a mala or contract. This requires practice but works wonderfully.
If none of this is working for you, or you'd like the selection process to come from an expert, you can always book a session with me to really dive into what it is your body is saying, and discover which gemstones are for you!