This isn't just for comics, but for fiction in general.
I am a sucker for desperate last stands, unlikely heroes and rag-tag bands of scrappy fighters facing impossible odds. And they don't even have to pull off miraculous victories for me to like it - I'm totally on board for inevitable doom, too. <3
Like, the Rohirrim at Helm's Deep, death-charging right into the army of Uruk-hai? Yeah, that's my cup of tea. Which is probably why I stuck with Steven Erikson's Malazan-books, despite their other flaws. Whatever else he might have gotten up to, he was great at impossible odds, desperate last stands and inevitable doom - with pinches of unlikely success. The Chain of Dogs/Coltain's March is one of my favourite pieces of fiction involving war.
As for more minor tropes... Like you, @epiale, I like size-differences in romance. I can't help it! Tiny and cute x Tall and intimidating is so adorable! I don't care about genders, either; whether it's a same-sex couple or a heterosexual couple, I don't mind. In fact, I think I'd like to see more size-difference straight couples where it's the male character who is small and cute, and the female character who is big and bulky. It'd be a nice change.
Also, villains trying to redeem themselves. People who, through the course of the story, realise that what they've been doing is wrong, and try to better themselves and make amends. Again, it's not important if they actually succeed; all that matters is that they try.