The comment around startups being short lived could raise an interesting possibility. If you're doing a type rating with them, maybe there is a bit of a gamble that if they were to go under, you could end up on the jobs market but with a valuable skillset behind you, one that is much more portable compared to doing a Fokker endorsement.
But yes, there is no objective answer there - you need to consider the factors that are important to you. Do you need/want the security of knowing that you'll have a long-term job with one employer, even if it means not progressing onto bigger and better things for a while? Or do you want to take what may seem a more risky path in the name of progressing quicker? Are you willing to relocate to pursue the opportunity? What is the culture like and how important is that to you? Those are the questions to ask yourself and then use that to get more specific and talk with people who are already flying with those airlines to see which one/s line up.