The verdict
For a small software team where a product manager needs answers without help from data people, I'd start with Mixpanel. It is quick to use on your own, and the free plan with a million events is large enough to learn on. I'd pick Amplitude if you want more under one roof, such as heatmaps and in-product guides, or if many people need seats and unlimited seats on every plan matters. Both are usage-based as you grow, and both need a tracking plan before you install anything. Since they are so close, run the same funnel in both before you decide.