Hi @Cornell333,
There are many ways to skin a cat. I have tasked myself with testing almost any available food out there available for shrimp. The short answer, 'best' is a very liberal term depending on what you are willing to spend on your shrimp. There are also many shrimp foods available such as all in one everyday foods, specialty, and supplemental. The truth is that you do not need any shrimp food at all if you have good biofilm supply as most vitamins, fatty acids and proteins are obtained from bacterial film directly.
It depends on what shrimp you have, and what you are willing to spend. You can have perfectly happy, healthy breeding shrimp in good condition on a generic store brand fish flake. If you want to specifically pay attention to fertility, exoskeletal health, colour etc there is a food out there to match and people have various and strong opinions about what works for them.
My personal opinion is that less is more. The less altered a product is, the more natural ingredient you are putting in your tank: it is more realistic that a dried organic nettle leaf falls into a pond naturally compared to a Pellet with glucomannan, synthesised vitamins etc.
I find shrimp keeping a very expensive hobby ( I might be doing it wrong!), so I prefer to pay a little extra to have peace of mind that my shrimp have the best odds of not developing deficiencies long term, because that would almost be impossible to identify. And losing shrimp for whatever reason hits you financially as buying new ones is not cheap- even cherries add up. So I try and give them the best odds.
Mosura, Benibachi, Shirakura are the most reputable and well known brands out there. The best quality brand of minimally altered products I have come across is the Dennerle Shrimp King range. In Australia, there is a locally owned brand called Boss Aquaria: the shrimp love the products I have tried ( and still have to review), and are made of natural ingredients that they disclose- I just have an issue with the ingredients that they are not disclosing on the packets ( I understand that it might be a copyright issue)- to be fair, most Asian market shrimp foods also do not disclose ingredients either. There are also pocket-friendly highly processed food like Fluval shrimp granules or Hikari: highly processed, but very nutritious and the manufacturer focuses on 'minimal waste'. As a person with biochemical background, I can confidently say that whichever option you choose, your shrimp will be fine as long as you give them variety and culture your biofilm ( that is a whole separate blog).
Compare shrimp feeding to dog feeding: all brands have one aim: to sell you their brand which they believe has its strong points and merits and is marketed to you that way.
The food review section on the forum has been going since 2012 and plenty of information available on there.
As to how much and how often: everyone has a different opinion as well. I find that feeding whatever they can eat in 3 hours max and then removing the remainder works really well, if you have starvation concerns you can always add shrimp snow as bacteria and fungus grow on the soy bean shells.
Good luck! ?