> Company B: I got an offer from another start-up like company, with a very interesting job, doing what I like. They pay: 3000 monthly for 40 hours a week, with 30 days paid vacation. Working here, would benefit my knowledge for my future plan greatly. I would not have that much spare-time between tasks.
I would note that 40 hour weeks, in my experience, are very rare in technical roles if you're at a "start-up like company". Be prepared for 60ish hour weeks (and celebrate if that doesn't happen).