This is the way I understand and see these 3 programs.

SBI was first and came up with the idea of being able to sponsor someone. This made it possible to get something for yourself and give something to someone else at the same time. While it's a good way to give something away in a contest, the numbers and fundamentals don't really add up to see it as an investment. New Shares need to be bough to fund old shareholders and the entire program would collapse if new money stopped coming in. It heavily relies on bought delegation and it's really hard to recover your initial investment.

Upvoteshares is a smaller scale 'proof of concept' system that is fully transparant and based on numbers which makes it all highly predictable. It is mostly aimed toward people who have a longer term mindset on Steemit and will benefit those the most. It also comes wit a way to sponsor minnows, but this is limited in time to make it scalable. Only minnows that get multiple sponsorships over time can also get permanent support in the form of a free (paid for by the program) upvoteshare. Basically the money and value comes from a minimum of 10% that is always powered up on top of what has been send and the shareholders that give up on steemit, this makes it also possible to distribute nearly all unused upvotes to other shareholders and grow the account making the shares worth more in price each level which benefits all existing shareholders.

Minnowbuilder is basically a project that aims to help minnows reach 500SP. Their concept is much better suited to do this in an organised way compared to SBI and Upvoteshares. It's less of an investment in yourself but more in the steemit platform whil you also get something for yourself at the same time.

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In short how I see these (feel free to correct me) SBI: Good if you host a contest and want to give out a price but purely as an investment it's a horrible deal and mainly helps the sbi accounts earn a lot of curation rewards. Upvoteshares: Good if you are a content creator that posts ~5+ posts weekly and in are on steemit for the long run. Mostly aimed to support yourself but also helps others at the same time. Minnowbuilder: Good if you look for an effective way to help minnow on this platform while also getting something for yourself at the same time.