Ask HN: How do you decide which “great opportunity from a friend” to work on?

So I now have two groups of friends who are wanting me to work on unrelated projects. I am the only person bringing coding chops to it. Both groups have good sales people that could sell the product once it was done.

I am in a rut in my day job and so I would like to work on both if I can because they would help increase my skillset. Both are greenfield projects so I can choose any code set to work with which means I can shore up skills that I don't have or have let languish. But I am not sure which project to go with.

One is a problem that is explained by the business as something that if solved would help on boarding of customers and be able to be cross sold to other business of the same type.

The other is a project that while the primary has thought it all out the target audience is aimed primarily at users who are not computer savvy.

I can provide more details, but I am curious what constraints or measuring sticks HN uses when pursuing a project that doesn't have an upside any time soon.