5. Colin Firth
Okay, so what if you don't want a comedic actor, but someone more in the vein of Christopher Eccleston? A dramatic performance, a powerhouse of dark acting? Consider then Colin Firth, one of the most renowned modern actors. He balances seamlessly between television and film, always giving an excellent performance. He's proven his skill at blending into a comedy role (Bridget Jones' Diary), family (Nanny McPhee), romantic (Pride and Prejudice), and finally dramatic, best demonstrated in his roles in A Single Man and later The King's Speech, both of which saw him be nominated for a Best Actor Oscar (and winning the latter). He's been receiving acclaim much earlier than that as well, with a BAFTA TV award nomination dating all the way back to 1988. While he's never strayed much into science fiction, there's no reason he wouldn't be good at it. And if he really puts himself into it, he could conquer the role.