Both, for sure.
If they're in the PHB, then they're in (and I'm saying this sight unseen; it's a principle that I'll make work, one way or another). Options in the DMG are not automatic. In the case of "Variants" within the PHB they'll I expect generally be used: of the variants in 5B, I like encumbrance, the alt-human, point-buy, spy, and skills with different abilities; playing on a grid will be used sometimes; and I am only hesitating on equipment sizes. If it's just one or two that are outliers, again I'll probably use them and make them work.
If they're in the PHB, then they're in (and I'm saying this sight unseen; it's a principle that I'll make work, one way or another). Options in the DMG are not automatic. In the case of "Variants" within the PHB they'll I expect generally be used: of the variants in 5B, I like encumbrance, the alt-human, point-buy, spy, and skills with different abilities; playing on a grid will be used sometimes; and I am only hesitating on equipment sizes. If it's just one or two that are outliers, again I'll probably use them and make them work.