Guts.
I feel like Griffith is the expected answer, and I almost said Griffith automatically, but no it is definitely Guts, and Griffith is really like, the opposite of a drama queen. He’s cool and collected to a fault. Even during the second duel – we saw his frantic thoughts, but he didn’t express them. He was cold, and rational enough that everyone there except Rickert and Casca thought his challenge was reasonable (including Guts). His reaction when Guts walked away was to slump into the snow and silently repress really hard. He was hallucinating and breaking from reality when he finally broke down over his post-torture situation – before that he was shockingly calm and chill about it, even at the moment he silently let his dream go. Fucking Charlotte was a terrible decision but it was a method of repression, and he was pretty calm and composed during, even making cute jokes.
He smiled calmly when he made the sacrifice.
His breakdown in the river in front of Casca was spoken calmly and he stopped and put on a fake smile the instant he realized how badly his mask had slipped. He casually referred to being taken advantage of by a child predator as “seducing an old man.” He was completely cold + polite + perfunctory when he killed Gennon. “Do you think I’m cruel?” was one of his more emotional moments and it was v quietly so. His replies to Guts asking why he risked his life for him were all v chill, either rationalizations or calm admittances of irrationality. His most emotional, unconsidered moment (other than like, the suicide attempt) was probably lifting his hand to strangle Guts in the torture chamber, and that came after a year of torture and brooding over Guts, and he immediately switched to holding his hand when Guts started crying lol. yk, etc etc etc.
I honestly can’t really imagine Griffith completely losing his self-control and throwing a drama queen type fit. He’s understated.
Guts on the other hand makes a big production out of everything. Guts loses control and declares wars to get a demon’s attention. Guts screams at ghosts, Guts threatens dudes by throwing severed heads at them, Guts cracks wise when he’s fighting people whether it’s in fun tournaments or in life or death situations, Guts loses control and strangles people, Guts lets people stab him when he’s upset, Guts cries a lot, Guts screams a lot, Guts makes dramatic bitter speeches a lot, Guts, let’s be honest, throws tantrums and lashes out at whoever happens to be nearby when he’s upset. He tells kids to kill themselves, tortures apostles when he’s extra mad, fights a hundred men because he just wants to swing his sword, exaggeratedly pouts when Casca is mean to him, rushes into battle before everyone else, and is honestly really, really self-centred in general imo. (Which, to be clear, is something I love about him. Guts’ brand of self-centredness is a gr8 flaw.)
Plus like canonically his central motivation for just about everything he does is wanting attention, specifically Griffith’s attention.
So yeah I would say Guts is by far way more of a drama queen than Griffith. Griffith completely downplays everything that affects him as much as humanly possible, while Guts thrives on melodrama and big emotional responses.
(tbh I wouldn’t exactly call Guts a drama queen either lol, he’s also p chill and understated about a lot of things, but compared to Griffith he totally is.)