Hey @Manah, those are great questions.

Someone actually did the math for this (although I can't remember specifics) and it turns out that the quadruple harvest fertilizer will land you more fruit over time than the growth fertilizer. However the quad fert does take slightly more effort since you have to replant every time you harvest.

As for the various plants and their usefulness, most plant products are used in at least two recipes, but some are used in more. I've ranked them here:

Trinuts: 4 Recipes (2 evobar ingredients, the Base Evobar which is used for all evobars, and the Decorative Item Potion).

Voxel Fruit: 3 recipes, all of them useful potions (Rarity Excluders and the Pixpet Potion), and you'll need a large quantity (8) for two of those potions

Evolution Fruit: 3 recipes (The juice is 1 recipe, and that's needed for 2 recipes. The Potion of Evolution is used in all evobars).

Tricolor Flower Petals: 3 recipes (3 evobar ingredients, one of them being the Color Reroll Bar which is very useful)

Mini Bananas: 3 recipes (The puree is 1 recipe, which is needed for 2 recipes including the Color Reroll Bar).

Giant Clover: 3 recipes (2 evobar ingredients and the Wealth Potion)

Blueberries: 3 recipes (2 evobar ingredients and the Special Ingredient Potion)

If I'm not mistaken (but someone please correct me), all other plant products are used in 2 recipes, as an evobar ingredient and a potion ingredient. I may edit my post to add them later, but for the most part the other potions aren't as important -- it really just depends on your current needs.

Let me know if anything I said was confusing or if you have more questions ^^