Which analytics service do you use when launching a product?

Segment is by far the BEST analytics platform when I was choosing. Still seems that way today.

Fathom Analytics works well and it doesn't collect personal or invasive data about its users.

First GA and then Matomo when my product shows traction

I always used: - Google tag manager to setup proper event tracking - Google analytics for the quantitative data and marketing attribution - Smartlook for the qualitative data and understand how people interact with the product.