How difficult is it to decide for your own future?
It's a month that I'm in total panic 'cause of a difficult choice I have to make about my job.
I really need some external opinions and points of view from other developers, maybe more experienced than me (I'm a medium-junior JS developer).

The situation is as follows:

1) I work as a Frontend Web Developer for a wonderful enterprise-like company with 100+ employees, where the individual rights are fully respected, there are no whatsoever pressures and there is a peaceful paradise-like atmosphere most of the days. I also love my teammates, which is something rare because I often dislike other humans.
2) I received a proposal from a Fintech startup, which required me a long time to complete a complex programming test they gave me. They look all very young, modern, fast and passioned about their job. But they are only living with bank's investments and are not producing any money at the moment. Also, I don't know if Fintech will be a successful field in the future.
3) I received another proposal, from a Healthtec startup this time, which has a lovely mission in the medical field, has received millions of investments, it's gaining some KK net each month but has a team of only 2 developers (3 with me if I accept). I know one of the developers and I remember he had issues of not getting paid months ago.

What's the problem with the first company? I totally dislike the product we are building, the development stack (fully Microsoft-based), the company's view (they still sell and think about software like in the 90's) and how the repository is managed. Everyday there are huge problems that end up blocking the frontend work and the final product is super ugly and works only if you know all the quirks behind it.
It's an old-fashioned desktop app with inside Chromium which should execute some components like graphs, tables, forms and shit like this. Every component is configurable through a property editor which is an utter giant mess of collapsed menus. I also suspect that the company's main business model is based on the difficulty to use this software (because they sell licenses and courses to use it).
There are no modern UX/UI concepts applied at all, nor they seem to care about it.
Each time I propose something there is a huge chain of approval-waiting that end up in a stale mate.
Also, it's useless to show my frustration about all these issues because I count very little in a so populated office.

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TLDR: I need to choice if staying in a Enterprise Microsoft-based and old-fashioned company, but in which the atmosphere is paradisiac or accept the risk to work for a Fintech or a Healthtec startup.
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What would you do if you were in my situation? What's for you the most stable field in the future?
Many thanks for the attention!