1. The costumes are often more varied ("tough" costumes show up for both genders; "soft" costumes tend to be only for females).
2. In at least some cases (City of Heroes was a classic), female characters just move more gracefully / naturally than male ones.
3. I personally find male heroic figures to be so overdone (being a regular comic book reader) that female heroic figures are just more interesting to me to play (often the case of my comic book reading, too).
(h/t +Les Jenkins)
The Surprisingly Unsurprising Reason Why Men Choose Female Avatars in World of Warcraft
When men play female avatars in online games, they change the way they speak to conform to female stereotypes—but the way they move betrays their masquerade. In a recent study reported in Information, Communication and Society, researchers created a custom-built quest in World of Warcraft—the popular online game where players…
What does this say about me choosing to play as a dwarf priest?
"… I'll be in my bunk …"
Yeah, all of my characters except for one were female, and my main was a Night Elf Warrior in World of Warcraft.
1) Pretty to look at (sex appeal)
2) smaller stature than males of the same race (better field of view)
It's mostly the first one. If I'm going to stare at a character for hours on end, I'd prefer it be a woman.
Plus, in fantasy settings, I've always had tremendous respect for strong women (which is why I adore Brienne of Tarth, which I'm sure I'll regret, eventually).
Of my mains in CoH, discounting a huge or two, probably 80% were female. My main main was male, but essentially a Mary Sue of me. My only other significant male character was an intentional husband-and-wife combo with, well, my wife.