The verdict
Start with how your revenue arrives. If calls drive your leads and you spend on ads, I'd pick CallRail. If an affiliate or partner programme already brings meaningful revenue and a spreadsheet no longer copes, I'd pick Trackdesk.
For a first affiliate test, Trackdesk is too much. Its plan limits and set-up assume an existing programme. For a business with no phone step, CallRail is not needed either.
So this is rarely a real contest. Pick the one that matches your channel today. If you need both, they do not overlap, so you can add the second one later without a clash.