Does Gaea's Cradle tap for mana equal to creatures you control or creatures in play?

Gaea's Cradle reads: '{T}: Add {G} for each creature you control.' The word 'you' refers specifically to the player who controls Gaea's Cradle and is activating its ability. Creatures controlled by your opponents do not count. This is governed by the general rule that 'you' in a card's text always refers to that object's controller (CR 109.5).

Mana abilities like Gaea's Cradle are activated abilities that produce mana, defined under CR 605.1. They resolve immediately without using the stack in most contexts, but the counting of creatures you control is evaluated at the time the ability resolves (CR 605.3b).

It's important to note that since the rules update that removed the concept of 'the battlefield' being called 'in play,' any older discussion of 'creatures in play' simply means creatures on the battlefield (CR 400.1). But regardless of terminology, only YOUR creatures on the battlefield count.

Example: You control Gaea's Cradle and 4 creatures. Your opponent controls 6 creatures. When you tap Gaea's Cradle, you add {G}{G}{G}{G} — four green mana — not ten.

If a creature you control leaves the battlefield in response to the mana ability being activated (note: mana abilities don't use the stack, so this scenario is rare), the count is taken at resolution. Tokens and non-token creatures both count equally as long as you control them.