Which of these main characters do you sympathize with more. Cold-blooded and determined or lively and playful. And why? (I know there are other aspects of the character, I'm just curious about these particular cases.)
Cold-Blooded and determined because I am cold-blooded and determined.
Yes, I can be Lively and playful, but when the SHTF I drop the fun like a bad habit, and shit gets DONE. It really depends on the situation, because being lively and playful is what I DO to get shit done. When you are dealing with the mentally disabled and they are losing their shit, they become a mirror of you. If staff is having a bad day, they are having a bad day. If you are upset, they get upset. If you are afraid, they are afraid.
So when the building gets snowed in and you are down one staff and it's you and one person with no help coming and there is frickin' thunder snow (I honestly think there is no weather more terrifying than thunder snow.) and you are trapped for 4 days straight, being happy, smiley, and optimistic means the clients have no fear and thus no problems.
You would be surprised how often a situation can be solved just by acting like a fool. Everyone is laughing and all you had to do is crack some jokes and act stupid? I'll do that in a heartbeat. I don't care what people think. I know what I am and what I can do and not one shred of my self-esteem depends on what you think. I am someone at the age of 50 you can drop into the middle of a disaster and I will fix things and get everyone out of trouble. At least once. I might kill myself, but it'll get done.
But I promise you, when the margin for error vanishes and you need to get shit done NOW, I don't feel a thing until AFTER the disaster is fixed. Then I might have a panic attack. There was a situation where I don't even remember how I got everyone out of trouble. I just did it. Asshole blew up his house, set the group home on fire with the debris, everyone was on the street before the other staffer got out of the bathroom. Fortunately, it only scorched the roof.
Then I was over to see what I could do across the street, but alas, it was one of those, Nobody walking out situations. The whole time the other staffer was just screeching, "Oh My God". The Evac was actually unneeded, but I felt better with the clients all safely locked up in the Van than in the house.
If your MC is happy all the time and doesn't take anything seriously, the reader won't.