In practice you will end up using more than one, and that is normal rather than a failure of standardisation. Clients will send you invitations on their platform, and joining as a guest through a browser is usually possible without an account. What you need is one you host on, chosen because it works reliably and is easy for a guest to join, plus a willingness to use whatever somebody else sends you.
The free tiers are sufficient for most first year businesses, with one common exception. Several impose a time limit on group calls, typically around forty minutes, which is fine for a scheduled check in and disruptive during a longer working session. If your calls routinely run past that, the paid tier of whatever you already use is a smaller decision than switching platforms.
Two features are worth having and often overlooked. Recording, because a client conversation you can revisit is more useful than notes taken while trying to listen, provided you say clearly that you are recording and get agreement. And a stable joining link that does not change, which removes an entire category of small administrative friction if you meet the same people repeatedly.
The thing that actually affects how these calls go is not the software. It is a wired connection where possible, a microphone that is not the one built into your laptop, and light coming from in front of you rather than behind. Those three cost very little and make a larger difference to how you come across than any platform choice.
Set up your side once and stop thinking about it, because the variables that affect how a call goes are physical rather than software. A position where light falls on your face rather than behind you, a camera at eye level, and a microphone that is not the one in your laptop cover almost all of it. Those three take an afternoon to arrange and improve every call afterward, which is a considerably better return than any comparison of features between platforms.
Have a fallback and know what it is before you need it. Calls fail, and the difference between a minor interruption and a lost meeting is whether both parties know what happens next. A line in your calendar invitation giving your phone number, and a habit of switching to a call rather than spending ten minutes troubleshooting, resolves most of it. For client work particularly, the person who calmly moves to a phone call reads as competent while the person still restarting their application does not.