From the Ixalan set, we received double faced cards with lands on the back. I believe they count as all types on both sides while not on the field. Therefore:
When Golos, Tireless Pilgrim activates his ETB and I pick Gold-Forge Garrison as my land, which side does it enter as?
Double-faced cards only count as their front face while not on the battlefield. From the rules on double-faced cards:
711.4a While a double-faced card is outside the game, in a zone other than the battlefield, or on the battlefield with its front face up, it has only the characteristics of its front face.
You cannot choose Gold-Forge Garrison as your land, as its front face is not a land.
I think you're getting DFC rules mixed up with split cards, which do have the attributes of both halves while they're not being cast:
708.4 In every zone except the stack, the characteristics of a split card are those of its two halves combined. This is a change from previous rules.
A double-faced card always enters with its front face up unless it enters “transformed”. If you choose a double-faced card that is a land on its front face, like Westvale Abbey, Golos would not put it onto the battlefield transformed, so you would get the front face.
711.8 A double-faced card enters the battlefield with its front face up by default. If a spell or ability puts it onto the battlefield “transformed,” it enters the battlefield with its back face up.
The Ixalan double faced cards are not treated as lands unless they are on the battlefield and transformed.
711.4a While a double-faced card is outside the game, in a zone other than the battlefield, or on the battlefield with its front face up, it has only the characteristics of its front face.
