In Plants vs. Zombies 2, the single sunflower costs 50 sun, while the double sunflower costs 125. With 1x initial sun upgrade which gives 75 sun when a level begins (obtainable in one of the side branches), you can wait for 2 normal sun drops and you can build a single Double Sunflower. Or you can plant 2 single sunflowers in swift succession, which costs 25 sun less
If there are no space constraints, and if you have the potato mine (which let you drag the out beginning of the level while waiting for more suns), which will provide more sun over time (after factoring the costs of the sunflowers)?