Free Spins Conditions

I keep coming across casino promotions featuring bonus codes and free spins, but the conditions seem to be written differently on every website. For those who have more experience, which factors do you consider most important when comparing these offers? Do you focus on the advertised bonus size, wagering requirements, validity period, minimum deposit, maximum winnings or withdrawal restrictions? I’d like to understand the differences before registering rather than simply choosing the promotion with the biggest number of free spins.